LLVMLINUX: DO-NOT-UPSTREAM arm64, LLVMLinux: prfm

Fix for prfm error on AArch64

The following error is generated with the mainline clang compiler
for AArch64:

arch/arm64/include/asm/processor.h:149:15:
error: invalid operand in inline asm: 'prfm pldl1keep, ${0:a}
'

Per comments by Tim Northover on the LLVM Bug database:

"It's rather unclear how it's better than "prfm pstl1keep, [%0]" though.
Not all instructions can make use of any offset, so wouldn't we have to be
conservative and always map it to "[xN]"?

When %a0 is changed to [%x0] it uncovered a GCC bug:
https://bugs.linaro.org/show_bug.cgi?id=635



Changing the "p" to "r" resolves the issue for both clang and GCC.

Change-Id: I833620cb2ed7ebb0bbd25da3b77624e06fe46a85
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Git-commit: c3212ac08fa69652a7f8fb60121a9721d9a441d3
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>