loader(aarch64 el1): pop stack properly

Need to pop the stack only once in el1_mmu_disable,
and twice in el1_mmu_enable as we pushed once and twice
respectively. Not sure how these got switched.

Signed-off-by: Julia Vassiliki <julia.vassiliki@unsw.edu.au>

Author: midnightveil

loader/src/aarch64/util64.S

@@ -302,7 +302,6 @@ BEGIN_FUNC(el1_mmu_disable)
      */
     bl      invalidate_icache
 
-    ldp     x27, x28, [sp], #16
     ldp     x29, x30, [sp], #16
     ret
 END_FUNC(el1_mmu_disable)
@@ -372,6 +371,7 @@ BEGIN_FUNC(el1_mmu_enable)
 
     enable_mmu sctlr_el1, x8
 
+    ldp     x27, x28, [sp], #16
     ldp     x29, x30, [sp], #16
     ret