ArmPkg/CpuDxe: Disable interrupt before restoring context

ArmPkg/CpuDxe: Disable interrupt before restoring context

Interrupt must be disabled before we storing ELR and other system
registers, or else ELR will be overridden by interrupt reentrance.

This bug is critical as we may get occasional exception or dead loop
when interrupt reentrance occurs:

  After increasing SP ... Before popping out registers
Or
  After restoring ELR

The 1st circumstance could also be resolved by optimizing SP operation
(Pop out registers before adding SP back), but the 2nd could not be
resolved by disabling interrupt.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18538 6f19259b-4bc3-4df7-8a09-765794883524