treewide: Update fsl qspi node dt properties as per spi-mem driver

treewide: Update fsl qspi node dt properties as per spi-mem driver

According to new qspi driver, some properties like "bus-num, num-cs,
big-endian" are no longer used. Device endiannes can be determined from
device-type data in driver.

Now use board specific compatibles, generic node names and specific
labels to align with linux device-tree properties.

Also consolidate spi-max-frequency to 50Mhz treewide.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>