[SPARC64]: Fix sparse warnings in arch/sparc64/kernel/{cpu,setup}.c

We create a local header file entry.h, under arch/sparc64/kernel/,
that we can use to declare routines either defined in assembler
or only invoked from assembler.  As well as other data objects
which are private to the inner sparc64 kernel arch code.

Signed-off-by: David S. Miller <davem@davemloft.net>