arm64: efi: add missing frame pointer assignment

The prologue of the EFI entry point pushes x29 and x30 onto the stack but
fails to create the stack frame correctly by omitting the assignment of x29
to the new value of the stack pointer. So fix that.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/efi-entry.S

@@ -35,6 +35,7 @@ ENTRY(entry)
 	 * for image_addr variable passed to efi_entry().
 	 */
 	stp	x29, x30, [sp, #-32]!
+	mov	x29, sp
 
 	/*
 	 * Call efi_entry to do the real work.