usb: dfu: Enable progressive erase for MCUX FlexSPI flash

Devices using the MCUX FlexSPI flash driver erase their flash too
slowly, causing the usb stack to freeze, and USB DFU utilities to
report a timeout. Enable IMG_ERASE_PROGRESSIVELY for SOCs using the
MCUX FlexSPI driver to prevent this error.

Fixes #45359

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>