ArmPkg/CpuDxe: Exception Handling SP Adjust

The exception handling support code appears to adjust the stack pointer in the wrong direction.
It decrements the stack pointer by 0x60, but this should be an increment (add) for the
downward-growing stack.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eugene Cohen <eugene@hp.com>
Reviewed-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14646 6f19259b-4bc3-4df7-8a09-765794883524