MLK-21848-10 imx8qxp_mek: Update defconfig files for SPL

MLK-21848-10 imx8qxp_mek: Update defconfig files for SPL

1. Remove FIT support and enable TINY printf for saving SPL size.
2. Fix wrong SPL regulator driver enabled, show use fixed regulator not
   gpio.
3. Add flexspi defconfig which uses SPI relevant SPL configs and disable
   MMC, GPIO and regulator SPL drivers.
4. Enable the panic. Since we use PSCI to reset, but ATF is not boot when
   SPL is running.
5. Use full malloc not simple malloc which has dedicated malloc pool
   to support large pool size. The simple malloc size is also used by
   early malloc which occupies the stack space. This causes we can't
   have a large malloc pool

Signed-off-by: Ye Li <ye.li@nxp.com>