[U-Boot] mmc: Unirqify bcm2835_sdhost and fix writes

[Alexander Graf]

> The bcm2835 sdhost driver has a problem with "write multiple" commands.
> It seems to boil down to the fact that the controller dislikes its FIFO
> to get drained at the end of a block when a write multiple blocks command
> is in flight.
> 
> The easy fix is to simply get rid of all the IRQ driven logic and make
> the driver push as much data into the FIFO as it can. That way we never
> drain and we never run into the problem.
> 
> Reported-by: Jan Leonhardt <jan at cyberdesigner.net>
> Signed-off-by: Alexander Graf <agraf at suse.de>

Thanks, applied to rpi-next

Alex