boston: Move CM GCRs away from flash

Move the MIPS Coherence Manager (CM) Global Configuration Registers
(GCRs) away from the region of the physical address space which the
Boston board's parallel flash is found in, such that we can access all
of flash without clobbering GCRs.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>