firmware: convert Ambassador ATM driver to request_firmware()

Since it had various regions to be loaded to separate addresses, and it
wanted to do them in fairly small chunks anyway, switch it to use the
new ihex code. Encode the start address in the first record.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Acked-by: Chas Williams <chas@cmf.nrl.navy.mil>