arm64: zynqmp: Set qspi tx-buswidth to 4

In all the ZynqMP boards dts files tx-buswidth is by default set to 1. Due
to this the framework only issues 1-1-1 write commands to the GQSPI driver.
But the GQSPI controller is capable of handling 1-4-4 write commands, so
updated the tx-buswidth to 4 in ZynqMP boards dts files. This would enable
the spi-nor framework to issue 1-4-4 write commands instead of 1-1-1. This
will increase the tx data transfer rate, as now the tx data will be
transferred on four lines instead on single line.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/ad61199f55e5e00f29de6206d9d1872a52a7657e.1652193179.git.michal.simek@amd.com