Simplify management of SCTLR_EL3 and SCTLR_EL1

This patch reworks the manner in which the M,A, C, SA, I, WXN & EE bits of
SCTLR_EL3 & SCTLR_EL1 are managed. The EE bit is cleared immediately after reset
in EL3. The I, A and SA bits are set next in EL3 and immediately upon entry in
S-EL1. These bits are no longer managed in the blX_arch_setup() functions. They
do not have to be saved and restored either. The M, WXN and optionally the C
bit are set in the enable_mmu_elX() function. This is done during both the warm
and cold boot paths.

Fixes ARM-software/tf-issues#226

Change-Id: Ie894d1a07b8697c116960d858cd138c50bc7a069
diff --git a/lib/aarch64/xlat_tables.c b/lib/aarch64/xlat_tables.c
index d494112..ddc9ba8 100644
--- a/lib/aarch64/xlat_tables.c
+++ b/lib/aarch64/xlat_tables.c
@@ -329,8 +329,7 @@
 		isb();							\
 									\
 		sctlr = read_sctlr_el##_el();				\
-		sctlr |= SCTLR_WXN_BIT | SCTLR_M_BIT | SCTLR_I_BIT;	\
-		sctlr |= SCTLR_A_BIT;					\
+		sctlr |= SCTLR_WXN_BIT | SCTLR_M_BIT;			\
 									\
 		if (flags & DISABLE_DCACHE)				\
 			sctlr &= ~SCTLR_C_BIT;				\