microblaze: Fix BS=1 case

There was bug introduced by
"microblaze: Fix compilation error for BS=0"
(sha1: 50ef4f1128a880ea24c55b515125fc27cc489cf9)
which break compilation for BS=1 case.

Fixing is done in more generic way.
On systems without barrel shifter is bsrli replaced
by macro at build-time and replaced by srl instructions.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
microblaze: Add missing v8.50.a version

Add PVR value for MB 8.50.a.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
microblaze: extable: Sort the exception table at build time

Sort the exception table at build-time rather than during boot.

Microblaze is the same case as AARCH64 that's why
EM_MICROBLAZE conditional check was added to allow
cross-compilation on machines which are not running
the latest libc-dev.

Inspired by AARCH64 commit:
"arm64: extable: sort the exception table at build time"
(sha1: adace89562c7a9645b8dc84f6e1ac7ba8756094e)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>