tools/firmware: use a canned config for seabios

tools/firmware: use a canned config for seabios

The use of seabios defconfig kills boot performance of Windows guests
because the default is for the int13 handler to use PIO when accessing
the emulated IDE device.

By instead using a canned configuration with the ATA settings overridden
to enable DMA access (and also wider PIO) boot performance is markedly
improved without the need to use a different (and possibly not supported)
device model.

This patch adds the canned configuration into tools/firmware and modifies
the Makefile rule to copy it into place.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>