fpga: microchip-spi: separate data frame write routine

mpf_ops_write() function writes bitstream data to the FPGA by a smaller
frames. Introduce mpf_spi_frame_write() function which is for writing a
single data frame and use it in mpf_ops_write().

No functional changes intended.

Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20221230092922.18822-4-i.bornyakov@metrotek.ru


Signed-off-by: Xu Yilun <yilun.xu@intel.com>