spi: zynq_[q]spi: Use GENMASK macro

GENMASK macro used on zynq_spi.c and zynq_qspi.c

GENMASK is used to create a contiguous bitmask([hi:lo]).
Ex: (0x7 << 3) => GENMASK(5, 3)

Cc: Michal Simek <michal.simek@xilinx.com>
Acked-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>