doc: distro: Update list of all support boot types

Add HOST, UBIFS.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/develop/distro.rst b/doc/develop/distro.rst
index c522be6..0113a3d 100644
--- a/doc/develop/distro.rst
+++ b/doc/develop/distro.rst
@@ -295,7 +295,8 @@
 device or SD card) or type of boot device (e.g. USB disk). The parameters to
 the func macro (passed in by the internal implementation of the header) are:
 
-- Upper-case disk type (MMC, SATA, SCSI, IDE, USB, DHCP, PXE, VIRTIO).
+- Upper-case disk type (DHCP, HOST, IDE, MMC, NVME, PXE, SATA, SCSI, UBIFS, USB,
+  VIRTIO).
 - Lower-case disk type (same options as above).
 - ID of the specific disk (MMC only) or ignored for other types.