scripts: Add #! headers to shell scripts

Use /bin/sh by default.  The lists used in xtensa-build-all.sh are a
bash feature, use bash for that script.

Signed-off-by: Dylan Reid <dgreid@chromium.org>

scripts/host-build-all.sh

@@ -1,3 +1,5 @@
+#!/bin/sh
+
 # fail on any errors
 set -e
 

scripts/rimage-build.sh

@@ -1,3 +1,5 @@
+#!/bin/sh
+
 ./autogen.sh
 ./configure --enable-rimage
 make

scripts/xtensa-build-all.sh

@@ -1,3 +1,5 @@
+#!/bin/bash
+
 # fail on any errors
 set -e