fix(fvp): add optee specific mem-size attribute

Without the mem-size attribute, the OPTEE boot panics with below
error:
  |  get_sec_mem_from_manifest:1594 Can't read "mem-size" from FF-A
  |  		manifest at 0x6281000: error -1
  |  Panic at core/arch/arm/kernel/boot.c:1596 <get_sec_mem_from_manifest>
  |  TEE load address @ 0x6284000
  |  Call stack:
  |  0x0628c7fc
  |  0x06298788
  |  0x0628c480

Adding the mem-size attribute fixes the boot. This is OPTEE specific
extension.

Change-Id: I2801c8b4a89cffafff14c788319ad106b03ffef0
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
diff --git a/plat/arm/board/fvp/fdts/optee_sp_manifest.dts b/plat/arm/board/fvp/fdts/optee_sp_manifest.dts
index 749fbf6..84a7dd7 100644
--- a/plat/arm/board/fvp/fdts/optee_sp_manifest.dts
+++ b/plat/arm/board/fvp/fdts/optee_sp_manifest.dts
@@ -22,6 +22,7 @@
 	exception-level = <2>; /* S-EL1 */
 	execution-state = <0>; /* AARCH64 */
 	load-address = <0x6280000>;
+	mem-size = <0xd80000>; 	/* OP-TEE specific extension */
 	entrypoint-offset = <0x4000>;
 	xlat-granule = <0>; /* 4KiB */
 	boot-order = <0>;