Please support the native bios format for dec alpha

Currently qemu-system-alpha -bios parameter takes an ELF image.
However HP maintains firmware updates for those systems.

Some example rom files can be found here ftp://ftp.hp.com/pub/alphaserver/firmware/current_platforms/v7.3_release/DS20_DS20e/

It might allow things like using the SRM firmware.
The ARC(nt) firmware would allow to build and test windows applications for that platforms without having the relevant hardware