sys-boot/zfsbootmenu: initial import

Signed-off-by: Chaquen Beliakov Amaya <c@cgps.ch>

sys-boot/zfsbootmenu/files/zfsbootmenu-branding.patch

@@ -0,0 +1,20 @@
+--- a/etc/zfsbootmenu/config.yaml
++++ b/etc/zfsbootmenu/config.yaml
+@@ -3,14 +3,15 @@ Global:
+   BootMountPoint: /boot/efi
+   DracutConfDir: /etc/zfsbootmenu/dracut.conf.d
+ Components:
+-  ImageDir: /boot/efi/EFI/void
++  ImageDir: /boot/efi/EFI/gentoo
+   Versions: 3
+   Enabled: true
+   syslinux:
+     Config: /boot/syslinux/syslinux.cfg
+     Enabled: false
+ EFI:
+-  ImageDir: /boot/efi/EFI/void
++  ImageDir: /boot/efi/EFI/gentoo
++  Stub: /usr/lib/systemd/boot/efi/linuxx64.elf.stub
+   Versions: false
+   Enabled: false
+ Kernel: