Add QemuMacDrivers as submodule

The QemuMacDrivers project provides virtualisation drivers for PPC MacOS
guests.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

.gitmodules

@@ -34,3 +34,6 @@
 [submodule "roms/skiboot"]
 	path = roms/skiboot
 	url = git://git.qemu.org/skiboot.git
+[submodule "roms/QemuMacDrivers"]
+	path = roms/QemuMacDrivers
+	url = git://git.qemu.org/QemuMacDrivers.git

pc-bios/README

@@ -47,3 +47,6 @@
   (OpenPower Abstraction Layer) firmware for OpenPOWER systems. It can
   run an hypervisor OS or simply a host OS on the "baremetal"
   platform, also known as the PowerNV (Non-Virtualized) platform.
+
+- QemuMacDrivers (https://github.com/ozbenh/QemuMacDrivers) is a project to
+  provide virtualised drivers for PPC MacOS guests.

roms/QemuMacDrivers

@@ -0,0 +1 @@
+Subproject commit d4e7d7ac663fcb55f1b93575445fcbca372f17a7