Switch pc bios from pc-bios to seabios

SeaBIOS is a port of pc-bios to GCC.  Besides using a more modern tool chain,
SeaBIOS introduces a number of new features including PMM support, better
BEV and BCV support, and better PnP support.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "roms/seabios"]
 	path = roms/seabios
 	url = ../seabios.git
-[submodule "roms/pcbios"]
-	path = roms/pcbios
-	url = ../pcbios.git

pcbios @ da5ff65d

-Subproject commit da5ff65dc9473e3f069736d38b9a189ea14a67eb