context_mgmt: Fix MISRA defects

The macro EL_IMPLEMENTED() has been deprecated in favour of the new
function el_implemented().

Change-Id: Ic9b1b81480b5e019b50a050e8c1a199991bf0ca9
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/plat/arm/common/execution_state_switch.c b/plat/arm/common/execution_state_switch.c
index b12d82c..8fa864d 100644
--- a/plat/arm/common/execution_state_switch.c
+++ b/plat/arm/common/execution_state_switch.c
@@ -117,7 +117,7 @@
 		 * Switching from AArch64 to AArch32. Ensure this CPU implements
 		 * the target EL in AArch32.
 		 */
-		impl = from_el2 ? EL_IMPLEMENTED(2) : EL_IMPLEMENTED(1);
+		impl = from_el2 ? el_implemented(2) : el_implemented(1);
 		if (impl != EL_IMPL_A64_A32)
 			goto exec_denied;