flash_clear_pgperr_flag is a name used on f247, which is actually most
analogous to the SIZERR bit on l4, (it's a parallelism error)
the bit being cleared originally in this function, PROGERR is a new bit,
and should have it's own name.
Add a function to handle the previously unhandled size/parallelism flag,
and rename the existing one to properly reflect it's new name.
ddc7ab8c6c