sparc64: Cleanups and corrections for arch/sparc64/Kconfig

Refer to chip as "SPARC" throughout.

Say 32-bit SPARC and 64-bit SPARC rather than mentioning specific
chips such like UltraSPARC, as appropriate.

Remove non-sense help text referring to things that will never appear
on a SPARC system, such as EISA busses etc.

Use "help" instead of "--help--"

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