meta-bletchley: introduce Bletchley common functions

Add a common functions script for reusing the functions which are
called frequently.

This patch depends on the patchs below:
* https://lore.kernel.org/all/20220613095150.21917-4-potin.lai.pt@gmail.com/

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Change-Id: I6e1602b00f1b0a19e77506be6eabe18c796e52fe
diff --git a/meta-facebook/meta-bletchley/recipes-bletchley/plat-svc/plat-svc_0.1.bb b/meta-facebook/meta-bletchley/recipes-bletchley/plat-svc/plat-svc_0.1.bb
index 99af81d..23b2d1f 100644
--- a/meta-facebook/meta-bletchley/recipes-bletchley/plat-svc/plat-svc_0.1.bb
+++ b/meta-facebook/meta-bletchley/recipes-bletchley/plat-svc/plat-svc_0.1.bb
@@ -5,6 +5,7 @@
 
 RDEPENDS:${PN} += "bash"
 RDEPENDS:${PN} += "libgpiod-tools"
+RDEPENDS:${PN} += "bletchley-common-functions"
 
 SRC_URI += " \
     file://bletchley-early-sys-init \