Add standby state support in PSCI cpu_suspend api ...

This patch adds support in the generic PSCI implementation to call a
platform specific function to enter a standby state using an example
implementation in ARM FVP port

Fixes ARM-software/tf-issues#94
Change-Id: Ic1263fcf25f28e09162ad29dca954125f9aa8cc9

Remove partially qualified asm helper functions ...

Each ARM Trusted Firmware image should know in which EL it is running
and it should use the corresponding register directly instead of reading
currentEL and knowing which asm register to read/write

Change-Id: Ief35630190b6f07c8fbb7ba6cb20db308f002945

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