microblaze: nommu: Don't clobber R11 on syscalls

The noMMU syscall trap has a bug that causes R11 to be zero on return to
userland. Remove the extra "save" of R11 responsible for the bug.

Remove reloading of mode indicator because r11 already contains it.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>