microblaze: generate uapi header and system call table files

System call table generation script must be run to gener-
ate unistd_32.h and syscall_table.h files. This patch will
have changes which will invokes the script.

This patch will generate unistd_32.h and syscall_table.h
files by the syscall table generation script invoked by
microblaze/Makefile and the generated files against the
removed files must be identical.

The generated uapi header file will be included in uapi/-
asm/unistd.h and generated system call table header file
will be included by kernel/syscall_table.S file.

Signed-off-by: Firoz Khan <firoz.khan@linaro.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>