drivers: nxp: flexspi: fix hyper flash hang issue

CS hold time parameter is not correct which may cause bus fault
randomly.
System hang during status register reading after flash progromming which
is caused by parameter accessing in XIP mode.
Add dummy delay for READ command according the flash datasheet which is
required for SDR mode.
Use FlexSPI internal divider for clock updating instead of register in
CCM to avoid potential risk caused by flash access during clock updating
procedure.

Signed-off-by: Raymond Lei <raymond.lei@nxp.com>