xbmk: use sbase sha512sum, not host sha512sum

the --status flag seems to be a GNUism

as stated in the previous commit, i import sbase
suckless now, so as to have a consistent implementation
of sha512sum.

this ensures that its output is reliable, when i'm using
the output of this command within backticks.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/init.sh

@@ -35,11 +35,14 @@ checkvarschk=""
 is_child=""
 basetmp=""
 
+sha512sum="util/sbase/sha512sum"
+
 xbmk_init()
 {
 	xbmkpwd="`pwd || err "Cannot generate PWD"`" || err "!" xbmk_init "$@"
 	xbmklock="$xbmkpwd/lock"
 	basetmp="$xbmkpwd/xbmkwd"
+	sha512sum="$xbmkpwd/util/sbase/sha512sum"
 
 	if [ $# -gt 0 ] && [ "$1" = "dependencies" ]; then
 		x_ xbmkpkg "$@"