system-arm: AArch64 boot, init CNTFRQ_EL0

CNTFRQ_EL0 should be initialised to a uniform value in all cores present
in the system. Previously, this was only done if EL3 was present,
however architecture states CNTFRQ_EL0 may be written from the highest
EL implemented.
This patch moves this initilization outside of the EL3-only one.

Change-Id: Ibaa197de53d531ba898e5137ba4f46a8c9554699
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24683
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

system/arm/bootloader/arm64/boot.S

@@ -40,6 +40,8 @@
 
         .globl	_start
 _start:
+        ldr	x0, =CNTFRQ
+        msr	cntfrq_el0, x0
         /*
          * EL3 initialisation
          */
@@ -55,9 +57,6 @@ _start:
 
         msr	cptr_el3, xzr			// Disable copro. traps to EL3
 
-        ldr	x0, =CNTFRQ
-        msr	cntfrq_el0, x0
-
         /*
          * Check for the primary CPU to avoid a race on the distributor
          * registers.
@@ -180,10 +179,6 @@ start_ns:
         str	wzr, [x4, #0xa0]		// V2M_SYS_CFGDATA
         str	w5, [x4, #0xa4]			// V2M_SYS_CFGCTRL
 
-        // set up the arch timer frequency
-        //ldr	x0, =CNTFRQ
-        //msr	cntfrq_el0, x0
-
         /*
          * Primary CPU
          */