feat(cm): add explicit context entries for ERRATA_SPECULATIVE_AT

* Currently, "ERRATA_SPECUALTIVE_AT" errata is enabled by default
  for few cores and they need context entries for saving and
  restoring EL1 regs "SCTLR_EL1 and TCR_EL1" registers at all times.

* This prevents the mechanism of decoupling EL1 and EL2 registers,
  as EL3 firmware shouldn't be handling both simultaneously.

* Depending on the build configuration either EL1 or EL2 context
  structures need to included, which would result in saving a good
  amount of context memory.

* In order to achieve this it's essential to have explicit context
  entries for registers supporting "ERRATA_SPECULATIVE_AT".

* This patch adds two context entries under "errata_speculative_at"
  structure to assist this errata and thereby allows decoupling
  EL1 and EL2 context structures.

Change-Id: Ia50626eea8fb64899a2e2d81622adbe07fe77d65
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
diff --git a/include/arch/aarch64/el3_common_macros.S b/include/arch/aarch64/el3_common_macros.S
index b4c5c1b..60c5a0c 100644
--- a/include/arch/aarch64/el3_common_macros.S
+++ b/include/arch/aarch64/el3_common_macros.S
@@ -437,7 +437,7 @@
 	 * -----------------------------------------------------------
 	 */
 	isb
-	ldp	x28, x29, [sp, #CTX_EL1_SYSREGS_OFFSET + CTX_SCTLR_EL1]
+	ldp	x28, x29, [sp, #CTX_ERRATA_SPEC_AT_OFFSET + CTX_ERRATA_SPEC_AT_SCTLR_EL1]
 	msr	sctlr_el1, x28
 	isb
 	msr	tcr_el1, x29