p2b_ls/p3b_f boards: no payload and no vga init

The configs were enabling SeaBIOS payload, but this is to be
handled by lbmk, not coreboot.

Further, they were enabling VGA ROM execution in coreboot, but
this should be handled by SeaBIOS.

This board should not have a GRUB payload enabled either; this
will be checked and fixed if necessary in the next commit.