sparc32: Remove sun4 and sun4c from enum sparc_cpu.

All the remaining references are trivially removed since we've
just eliminated the final reference to sparc_cpu_model from
assembler code in commit b7d96ce189564e661909fbf8df39d7358149885b
("sparc32: Remove sparc_cpu_model read from floppy interrupt handler.")

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