[seabios] Add recipe for 1.7.5.

Port relevant patches and move to an earlier version.  Use release
tarball instead of a git repo copy.  Do not build the video bios (it is
not shipped in hvmloader anyway).
[vgabios] Standalone recipe for v0.7a

Plex86/Bochs vgabios version 0.7a.
Port patches from Xen's tree.
Add our relevant patches on top.

We used to ship in hvmloader the same bios (earlier version) from Xen's
tree.
[xen-firmware] Use out of tree vgabios.

Use vgabios out-of-tree with its own patches taken out of xen's
tree.
[stubdomain-initramfs] Add rsyslog.

Qemu and its helpers are logging in syslog. So we might as well have
rsyslog redirecting everything to hvc0 for consistency.
[qemu-dm] Use instead of ioemu.

dm-agent initscript uses -q option.
stubdomain initscript runs dm-agent -q.
stubdomain initscript runs qemu-ifup to setup bridges.
stubdomain initramfs depends on qemu-dm.
dom0 task depends on qemu-dm.
[linux-patches] gem-foreign, silence debug logs.

Remove loud debug output from the GEM patch.