MIPS: SiByte: Bring back cache initialisation

Bring back cache initialisation for Broadcom SiByte SB1 cores, which has
been removed causing the kernel to hang at bootstrap right after:

Dentry cache hash table entries: 524288 (order: 8, 4194304 bytes, linear)
Inode-cache hash table entries: 262144 (order: 7, 2097152 bytes, linear)

The cause of the problem is R4k cache handlers are also used by Broadcom
SiByte SB1 cores, however with a different cache error exception handler
and therefore not using CPU_R4K_CACHE_TLB:

obj-$(CONFIG_CPU_R4K_CACHE_TLB) += c-r4k.o cex-gen.o tlb-r4k.o
obj-$(CONFIG_CPU_SB1)           += c-r4k.o cerr-sb1.o cex-sb1.o tlb-r4k.o

(from arch/mips/mm/Makefile).

Fixes: bbe4f634 ("mips: fix r3k_cache_init build regression")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v6.8+
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>