microblaze: Fix bug with mmap2 syscall MB implementation

Fix mmap2 behaviour which incorrectly works with pgoff
not in 4k units.

Reported-by: Rich Felker <dalias@aerifal.cx>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

diff --cc arch/microblaze/kernel/sys_microblaze.c
Simple merge

diff --cc arch/microblaze/kernel/syscall_table.S
Simple merge