remove empty definition of display_boot_progress()

This patch replaces the empty definition of display_boot_progress() in
bl2_main.c with a weak definition. The former allowed bl2 to use the
early_exceptions(). It is possible to do that with a simple weak
definition as well.

Change-Id: Idb3f425a5e265f3579b638e3d26bd8c9bb78f80d
Build system: Fixes #2: Add multi-platform support

Move all explicit platform or architecture specific references
into a new platform.mk file that is defined for each platform.

Change-Id: I9d6320d1ba957e0cc8d9b316b3578132331fa428
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
Build system: minor spacing tidyup

Tidy up the spacing of variable definitions within the makefiles to make
them more consistent, easier to read and amend.

Change-Id: Ic6d7c8489ca4330824abb5cd1ead8f1d449d1a85
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
Build system: add 'make help' option

Add the 'help' target to the Makefile to present a brief guide to the
various build options available.

Change-Id: Ic3a3489860b6362eb236470ea6b43a16a1b2fe3a
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
fvp: rename fvp_* files to plat_*

The FVP platform has a few filenames that begin with fvp_.  These are
renamed to plat_ to make it easier to use the FVP port as a template.

Change-Id: I601e6256d5ef3bae81a2e1f5df6de56db5b27069
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>
psci: replace secure context with suspend context

The secure context saved and restored across a cpu_suspend operation
can be more than just the state of the secure system registers e.g. we
also need to save the affinity level till which the cpu is being
powered down. This patch creates a suspend_context data structure
which includes the system register context. This will allow other bits
to be saved and restored as well in subsequent patches.

Change-Id: I1c1f7d25497388b54b7d6ee4fab77e8c6a9992c4
psci: preserve target affinity level during suspend

This patch adds support to save and restore the target affinity level
specified during a cpu_suspend psci call. This ensures that we
traverse only through the affinity levels that we originally intended
to after resuming from suspend.

Change-Id: I0900ae49a50b496da137cfec8f158da0397ec56c
psci: fix affinity level upgrade issue

The psci implementation does not track target affinity level requests
specified during cpu_suspend calls correctly as per the following
example.

1. cpu0.cluster0 calls cpu_suspend with the target affinity level as 0
2. Only the cpu0.cluster0 is powered down while cluster0 remains
   powered up
3. cpu1.cluster0 calls cpu_off to power itself down to highest
   possible affinity level
4. cluster0 will be powered off even though cpu0.cluster0 does not
   allow cluster shutdown

This patch introduces reference counts at affinity levels > 0 to track
the number of cpus which want an affinity instance at level X to
remain powered up. This instance can be turned off only if its
reference count is 0. Cpus still undergo the normal state transitions
(ON, OFF, ON_PENDING, SUSPEND) but the higher levels can only be
either ON or OFF depending upon their reference count.

The above issue is thus fixed as follows:

1. cluster0's reference count is incremented by two when cpu0 and cpu1
   are initially powered on.

2. cpu0.cluster0 calls cpu_suspend with the target affinity level as
   0. This does not affect the cluster0 reference count.

3. Only the cpu0.cluster0 is powered down while cluster0 remains
   powered up as it has a non-zero reference count.

4. cpu1.cluster0 call cpu_off to power itself down to highest possible
   affinity level. This decrements the cluster0 reference count.

5. cluster0 is still not powered off since its reference count will at
   least be 1 due to the restriction placed by cpu0.

Change-Id: I433dfe82b946f5f6985b1602c2de87800504f7a9