spi: drop "select SPI_MASTER_OF"

There is no Kconfig symbol named SPI_MASTER_OF. The select statement for
that symbol is a nop. Drop it.

While we're touching that Kconfig entry also drop a superfluous
dependency on SPI (this entry is wrapped in "if SPI" / "endif").

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>