sparc: unify kernel/cpu

o use cpu_32.c as base
o move all sparc64 definitions to the common cpu.c
o use ifdef for the parts that differs and use cpu_32 as base
o spitfire.h required a CONFIG_SPARC64 guard to fix build on 32 bit

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>