spi: sirf: drop redundant sirf,marco-spi compatible string

"sirf,marco-spi" is redundant as all SPI controllers in CSR SiRFSoC are
compatible with prima2-spi.
at the same time, the whole marco project was dropped and its replacement
atlas7 is also compatible with prima2 in SPI.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Mark Brown <broonie@kernel.org>