cxl: Use image state defaults for reloading FPGA

Select defaults such that a PERST causes flash image reload.  Select which
image based on what the card is set up to load.

CXL_VSEC_PERST_LOADS_IMAGE selects whether PERST assertion causes flash image
load.

CXL_VSEC_PERST_SELECT_USER selects which image is loaded on the next PERST.

cxl_update_image_control writes these bits into the VSEC.

Signed-off-by: Ryan Grimm <grimm@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>