AArch32: Common changes needed for BL1/BL2

This patch adds common changes to support AArch32 state in
BL1 and BL2. Following are the changes:

* Added functions for disabling MMU from Secure state.
* Added AArch32 specific SMC function.
* Added semihosting support.
* Added reporting of unhandled exceptions.
* Added uniprocessor stack support.
* Added `el3_entrypoint_common` macro that can be
  shared by BL1 and BL32 (SP_MIN) BL stages. The
  `el3_entrypoint_common` is similar to the AArch64
  counterpart with the main difference in the assembly
  instructions and the registers that are relevant to
  AArch32 execution state.
* Enabled `LOAD_IMAGE_V2` flag in Makefile for
  `ARCH=aarch32` and added check to make sure that
  platform has not overridden to disable it.

Change-Id: I33c6d8dfefb2e5d142fdfd06a0f4a7332962e1a3
diff --git a/include/lib/aarch32/arch.h b/include/lib/aarch32/arch.h
index 6653cd1..aba15df 100644
--- a/include/lib/aarch32/arch.h
+++ b/include/lib/aarch32/arch.h
@@ -191,6 +191,7 @@
 
 /* NASCR definitions */
 #define NSASEDIS_BIT		(1 << 15)
+#define NSTRCDIS_BIT		(1 << 20)
 #define NASCR_CP11_BIT		(1 << 11)
 #define NASCR_CP10_BIT		(1 << 10)