linux-postmarketos-allwinner: add exfat kernel module

Adding exfat kernel module support.

This boots and works as expected (I am able to read exfat disks) on my pinephone running pmOS v22.06.

I added via pmbootstrap kconfig edit, and just enabled the exfat module. I'd like to add this to stable but I can add it to edge first and wait for the service pack. This was performed from within a v22.06 chroot.