spi: zynqmp: gqspi: code cleanup and minor fixes

This patch updates ZynqMP Ultrascale+ GQSPI driver file for
following changes:

Code cleanup :
- Updated lines having length more than 80 characters
- Header file declarations are sorted in alphabetical order
- Changed variables containing numbers as 0X0.. to 0x0..
- Updated 0x00 to 0x0 at all places
- Mainly added/updated kernel documentation wherever required
- Updated comments for spell check and starting with capital letter
- Added new lines for making the code readable

Minor fixes:
- Removing return from function zynqmp_process_dma_irq()
- Added proper typecasting for some variables
- Removed magic numbers
- Added memcpy() in zynqmp_qspi_filltxfifo() function
- Updated goto targets in probe()

Signed-off-by: Ranjit Waghmode <ranjit.waghmode@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>