Set SCR_EL3.RW correctly before exiting bl31_main

SCR_EL3.RW was not updated immediately before exiting bl31_main() and
running BL3-3. If a AArch32 Secure-EL1 Payload had just been
initialised, then the SCR_EL3.RW bit would be left indicating a
32-bit BL3-3, which may not be correct.

This patch explicitly sets SCR_EL3.RW appropriately based on the
provided SPSR_EL3 value for the BL3-3 image.

Fixes ARM-software/tf-issues#126

Change-Id: Ic7716fe8bc87e577c4bfaeb46702e88deedd9895
Introduce convenience functions to build

This patch introduces two convenience functions to the build system:

  - assert_boolean: asserts that a given option is assigned either 0 or
    1 as values

  - add_define: helps add/append macro definitions to build tool command
    line. This also introduces the variable DEFINES which is used to
    collect and pass all relevant configurations to build tools

Change-Id: I3126894b034470d39858ebb3bd183bda681c7126
Reorganize build options

At present, various build options are initialized at various places in
the Makefile. This patch gathers all build option declarations at the
top of the Makefile and assigns them default values.

Change-Id: I9f527bc8843bf69c00cb754dc60377bdb407a951
Document summary of build options in user guide

Change-Id: I6bd077955bf3780168a874705974bbe72ea0f5f1
Add build configuration for timer save/restore

At present, non-secure timer register contents are saved and restored as
part of world switch by BL3-1. This effectively means that the
non-secure timer stops, and non-secure timer interrupts are prevented
from asserting until BL3-1 switches back, introducing latency for
non-secure services. Often, secure world might depend on alternate
sources for secure interrupts (secure timer or platform timer) instead
of non-secure timers, in which case this save and restore is
unnecessary.

This patch introduces a boolean build-time configuration NS_TIMER_SWITCH
to choose whether or not to save and restore non-secure timer registers
upon world switch. The default choice is made not to save and restore
them.

Fixes ARM-software/tf-issues#148

Change-Id: I1b9d623606acb9797c3e0b02fb5ec7c0a414f37e
Merge pull request #78 from jeenuv:tf-issues-148
Improve BL3-0 documentation

Provide some information about the expected use of BL3-0.

Fixes ARM-software/tf-issues#144

Change-Id: I5c8d59a675578394be89481ae4ec39ca37522750
Address issue 156: 64-bit addresses get truncated
Addresses were declared as "unsigned int" in drivers/arm/peripherals/pl011/pl011.h and in function init_xlation_table. Changed to use "unsigned long" instead
Fixes ARM-software/tf-issues#156
Merge pull request #85 from hliebel/hl/bl30-doc

Improve BL3-0 documentation
Merge pull request #83 from athoelke/at/tf-issues-126

Set SCR_EL3.RW correctly before exiting bl31_main
Merge pull request #91 from linmaonly/lin_dev

Address issue 156: 64-bit addresses get truncated