arch-arm: Rewrite the currEL helper method to use opModeToEL

Direct use of cpsr.el should be discouraged: it should be used when
in AArch64 only; when in AArch32 it won't return the matching EL.

Eg: when in Supervisor Mode (EL1), CPSR.M<3,0> (mode) is 0b0011,
and cpsr.el will return 0 (EL0)

Change-Id: I5504bd1f59980f79b2607cce435ea09245de12e5
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20249
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/utility.hh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2012-2013, 2016-2018 ARM Limited
+ * Copyright (c) 2010, 2012-2013, 2016-2019 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -153,8 +153,7 @@ currOpMode(ThreadContext *tc)
 static inline ExceptionLevel
 currEL(ThreadContext *tc)
 {
-    CPSR cpsr = tc->readMiscReg(MISCREG_CPSR);
-    return (ExceptionLevel) (uint8_t) cpsr.el;
+    return opModeToEL(currOpMode(tc));
 }
 
 /**