add support for squashing uid/gid in gen_initramfs_list.sh

Sometimes it is useful to squash all uid's/gid's to 0:0 regardless of current owner. For example, in build systems that get run as arbitrary users (uClinux-dist). This adds a special "squash" keyword so you can do '-g squash -u squash' and have ownership squashed to root.

---

index 683eb12..684fb9c 100644
@@ -19,11 +19,11 @@ $0 [-o <file>] [-u <uid>] [-g <gid>] {-d | 

<cpio_source>} ...
-o <file> Create gzipped initramfs file named <file> using
gen_init_cpio and gzip
-u <uid> User ID to map to user ID 0 (root).

-		       <uid> is only meaningful if <cpio_source>
-		       is a directory.
+		       <uid> is only meaningful if <cpio_source> is a
+		       directory.  "squash" forces all files to uid 0.
 	-g <gid>       Group ID to map to group ID 0 (root).
-		       <gid> is only meaningful if <cpio_source>
-		       is a directory.
+		       <gid> is only meaningful if <cpio_source> is a
+		       directory.  "squash" forces all files to gid 0.

<cpio_source> File list or directory for cpio archive.
If <cpio_source> is a .cpio file it will be used as direct input to initramfs.
@@ -113,8 +113,8 @@ parse() {
local gid="$4"
local ftype=$(filetype "${location}")

 	# remap uid/gid to 0 if necessary
-	[ "$uid" -eq "$root_uid" ] && uid=0
-	[ "$gid" -eq "$root_gid" ] && gid=0
+	[ "$root_uid" = "squash" ] && uid=0 || [ "$uid" -eq "$root_uid" ] && uid=0
+	[ "$root_gid" = "squash" ] && gid=0 || [ "$gid" -eq "$root_gid" ] && gid=0
 	local str="${mode} ${uid} ${gid}"

[ "${ftype}" == "invalid" ] && return 0