spi: xilinx_spi: Add support for spi memory operations

spi: xilinx_spi: Add support for spi memory operations

Add support for spi memory operations for xilinx AXI qspi driver.
This provides an high-level interface to execute SPI memory
operations by the controller.

Remove existing spi transfer based implementation and use
spi memory based exec_op() implementation for qspi IO operations.

Simplified existing startup_block implementation.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/1657954727-31972-2-git-send-email-ashok.reddy.soma@xilinx.com
Signed-off-by: Michal Simek <michal.simek@amd.com>