initrdscripts: Add the simplest init script

When booting from initramfs, one must provide a /init link.
This one is the simplest one, just forking a shell, allowing
for the smallest initramfs.

meta/packages/initrdscripts/files/init-boot.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+mkdir /proc
+mkdir /sys
+mount -t proc proc /proc
+mount -t sysfs sysfs /sys
+
+exec sh

meta/packages/initrdscripts/initramfs-boot_1.0.bb

@@ -0,0 +1,12 @@
+DESCRIPTON = "A live image init script"
+
+SRC_URI = "file://init-boot.sh"
+
+PR = "r0"
+
+do_install() {
+        install -m 0755 ${WORKDIR}/init-boot.sh ${D}/init
+}
+
+PACKAGE_ARCH = "all"
+FILES_${PN} += " /init "