floppy: Use timer_check() in floppy_wait_irq()

floppy: Use timer_check() in floppy_wait_irq()

Use timer_check() instead of using floppy_motor_counter in BDA for the
timeout check in floppy_wait_irq().

The problem with using floppy_motor_counter was that, after it reaches
0, it immediately stops the floppy motors, which is not what is
supposed to happen on real hardware. Instead, after a timeout (like in
the end of every floppy operation, regardless of the result - success,
timeout or error), the floppy motors must be kept spinning for
additional 2 seconds (the FLOPPY_MOTOR_TICKS). So, now the
floppy_motor_counter is initialized to 255 (the max value) in the
beginning of the floppy operation. For IRQ timeouts, a different
timeout is used, specified by the new FLOPPY_IRQ_TIMEOUT constant
(currently set to 5 seconds - a fairly conservative value, but should
work reliably on most floppies).

After the floppy operation, floppy_drive_pio() resets the
floppy_motor_counter to 2 seconds (FLOPPY_MOTOR_TICKS).

This is also consistent with what other PC BIOSes do.

Signed-off-by: Nikolay Nikolov <nickysn@users.sourceforge.net>