clk: gxbb: expose spifc clock

SPI clock is needed for the spifc driver, expose to DT
(and comment out in the clk driver)

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>