[MIPS] Clean Kernel headers are generated by running

libc/kernel/tools/update_all.py script. This patch ignores
any changes to libc/kernel directory not related to MIPS
architecture.

Change-Id: I2c9e461dccb7c33eb4420be2db1a562f45137c8d
Signed-off-by: Raghu Gandham <raghu@mips.com>
Signed-off-by: Chris Dearman <chris@mips.com>