floppy: Make sure to yield() during floppy PIO

The floppy Programmed IO code really should yield while the controller
is busy.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Minor - be consistent in placement of .code16/32 in romlayout.S

Place .code32 in those functions that need it, and make sure every
function ends in .code16 mode.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>