MdePkg/BaseLib: use normal register init in ARM SetJump implementations

There may be architectures on which there are benefits to
  eor r0, r0(, r0)
but ARM was never one of them. Change to more readable
  mov r0, #0
instead.

Signed-off-by: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

MdePkg/Library/BaseLib/Arm/SetJumpLongJump.S

@@ -33,7 +33,7 @@ GCC_ASM_EXPORT(InternalLongJump)
 ASM_PFX(SetJump):
   mov   r3, r13
   stmia r0, {r3-r12,r14}
-  eor   r0, r0, r0
+  mov   r0, #0
   bx    lr
 
 #/**

MdePkg/Library/BaseLib/Arm/SetJumpLongJump.asm

@@ -33,7 +33,7 @@
 SetJump
   MOV  R3, R13
   STM  R0, {R3-R12,R14}
-  EOR  R0, R0
+  MOV  RO, #0
   BX   LR
 
 ;/**