arm64: zynqmp: Dont use 4K sector size support for mini qspi configuration

This patch removes 4K sector size support for ZynqMP mini qspi
configuration in favour of fast erase speed.

Signed-off-by: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>