MIPS: kernel: cpu-probe.c: Add support for MIPS R6

Add MIPS R6 support when decoding the config0 c0 register.
Also add MIPS R6 support when examining the ebase c0 register
to get the core number and when getting the shadow set number
from the srsctl c0 register.

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>