powerpc/85xx: L2sram - Add compatible string to the device id list

The following platforms are supported:
mpc8544, mpc8572, mpc8536, p1021, p1025, p1024, p1010.

Signed-off-by: Tang Yuantian <Yuantian.Tang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>