[SPARC]: Kill 'prom_palette'.

The idea of this thing is we could save/restore the firmware's
palette when breaking in and out of the firmware prompt.

Only one driver implemented this (atyfb) and it's value is
questionable.  If you're just debugging you don't really
care that the characters end up being purple or whatever.

And we can provide better debugging and firmware command
facilities with minimal in-kernel console I/O drivers.

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