sparc: delete unused config symbols

There is no need to define a config symbol if
it is never set to any value. Undefined symbols equal
to 'n'.

GENERIC_GPIO looks like it is similar but
it is set using select in some other file so
it must be kept.

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