Add support for specifying pre-built BL binaries in Makefile

This patch adds support for supplying pre-built BL binaries for BL2,
BL3-1 and BL3-2 during trusted firmware build. Specifying BLx = <path_to_BLx>
in the build command line, where 'x' is any one of BL2, BL3-1 or BL3-2, will
skip building that BL stage from source and include the specified binary in
final fip image.

This patch also makes BL3-3 binary for FIP optional depending on the
value of 'NEED_BL33' flag which is defined by the platform.

Fixes ARM-software/tf-issues#244
Fixes ARM-software/tf-issues#245

Change-Id: I3ebe1d4901f8b857e8bb51372290978a3323bfe7
Merge pull request #210 from soby-mathew/sm/makefile_bl_stages

Add support for specifying pre-built BL binaries in Makefile
Initialize SCTLR_EL1 based on MODE_RW bit

Initializes SCTLR_EL1 based on MODE_RW bit in SPSR for the entry
point. The RES1 bits for SCTLR_EL1 differs for Aarch64 and Aarch32
mode.
Add opteed based on tspd

Adds a dispatcher for OP-TEE based on the test secure payload
dispatcher.

Fixes arm-software/tf-issues#239
Merge pull request #211 from jenswi-linaro/optee_140916

Dispatcher for OPTEE from Linaro SWG