Unify SCTLR initialization for AArch32 normal world

Unify SCTLR initialization for AArch32 normal world

The values of CP15BEN, nTWI & nTWE bits in SCTLR_EL1 are architecturally
unknown if EL3 is AARCH64 whereas they reset to 1 if EL3 is AArch32. This
might be a compatibility break for legacy AArch32 normal world software if
these bits are not set to 1 when EL3 is AArch64. This patch enables the
CP15BEN, nTWI and nTWE bits in the SCTLR_EL1 if the lower non-secure EL is
AArch32. This unifies the SCTLR settings for lower non-secure EL in AArch32
mode for both AArch64 and AArch32 builds of Trusted Firmware.

Fixes ARM-software/tf-issues#428

Change-Id: I3152d1580e4869c0ea745c5bd9da765f9c254947
Signed-off-by: Soby Mathew <soby.mathew@arm.com>