The Meson SPIFC driver uses regmap mmio functions and so it must
select REGMAP_MMIO to avoid the following build error:

spi-meson-spifc.c: undefined reference to `devm_regmap_init_mmio_clk'
Reported-by: NJim Davis <jim.epost@gmail.com>
Signed-off-by: NBeniamino Galvani <b.galvani@gmail.com>
Signed-off-by: NMark Brown <broonie@kernel.org>