Implement ARM Standard Service

This patch implements ARM Standard Service as a runtime service and adds
support for call count, UID and revision information SMCs. The existing
PSCI implementation is subsumed by the Standard Service calls and all
PSCI calls are therefore dispatched by the Standard Service to the PSCI
handler.

At present, PSCI is the only specification under Standard Service. Thus
call count returns the number of PSCI calls implemented. As this is the
initial implementation, a revision number of 0.1 is returned for call
revision.

Fixes ARM-software/tf-issues#62

Change-Id: I6d4273f72ad6502636efa0f872e288b191a64bc1
Implement standard calls for TSP

This patch adds call count, UID and version information SMC calls for
the Trusted OS, as specified by the SMC calling convention.

Change-Id: I9a3e84ac1bb046051db975d853dcbe9612aba6a9
Specify image entry in linker script

At present, the entry point for each BL image is specified via the
Makefiles and provided on the command line to the linker. When using a
link script the entry point should rather be specified via the ENTRY()
directive in the link script.

This patch updates linker scripts of all BL images to specify the entry
point using the ENTRY() directive. It also removes the --entry flag
passed to the linker through Makefile.

Fixes issue ARM-software/tf-issues#66

Change-Id: I1369493ebbacea31885b51185441f6b628cf8da0
Rework bakery lock with WFE/SEV sequence

Current implementation of Bakery Lock does tight-loop waiting upon lock
contention.

This commit reworks the implementation to use WFE instruction for
waiting, and SEV to signal lock availability. It also adds the rationale
for choosing Bakery Locks instead of exclusion primitives, and more
comments for the lock algorithm.

Fixes ARM-software/tf-issue#67

Change-Id: Ie351d3dbb27ec8e64dbc9507c84af07bd385a7df
Co-authored-by: Vikram Kanigiri <vikram.kanigiri@arm.com>