spi: cadence_qspi: Add support for page program using STIG write

spi: cadence_qspi: Add support for page program using STIG write

This patch supports page programming using STIG write. This is needed
if controller support only STIG writes for page program instead of
regular indirect write support. So, this patch gets the controller
capability from dt using "cdns,is-stig-pgm" property. This patch also
modifies stig write routine to support for page programming.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>