feat(arm): add trusty_sp_fw_config build option

Also increase add PLAT_ARM_SP_MAX_SIZE to override the default
ARM_SP_MAX_SIZE to support Trusty image and move OPTEE_SP_FW_CONFIG
documentation to build-internals.rst as it's not externally set-able.

Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ief90ae9113d32265ee2200f35f3e517b7b9a4bea
5 files changed