_targets: use metaelf to embedd integrity metadata

`metaelf` is utilized to add integrity checksums to all apps and
the kernel if it is intended to load as an ELF file (using the
"kernel" command instead of "kernelimg" which is for binary image
of kernel) and only when `phoenix-host-utils/metaelf` is available
(e.g., i.MXRT) or in custom projects.

JIRA: RTOS-296

_targets/build.common

@@ -191,6 +191,15 @@ b_add2img() {
 }
 
 
+b_signelf() {
+ # use metaelf to embed integrity checksum only when metaelf is available
+ if [ -f "$PREFIX_BUILD_HOST/prog.stripped/metaelf" ] && [[ "$1" != *.bin ]]; then
+ printf "Signing %s " "$1"
+ "$PREFIX_BUILD_HOST/prog.stripped/metaelf" -w "$1"
+ fi
+}
+
+
 b_prod_image() {
  b_log "Creating production images"
 
@@ -217,10 +226,12 @@ b_prod_image() {
 
  # Kernel
  OFFSET="$KERNEL_OFFS"
+ b_signelf "${PREFIX_PROG_STRIPPED}$KERNEL_FILE"
  b_add2img "${PREFIX_PROG_STRIPPED}$KERNEL_FILE" "$PHOENIX_DISK"
 
  # Programs
  for prog in "${PROGS[@]}"; do
+ b_signelf "${PREFIX_PROG_STRIPPED}$prog"
  b_add2img "${PREFIX_PROG_STRIPPED}$prog" "$PHOENIX_DISK"
  done
 
@@ -237,10 +248,12 @@ b_kernel_image() {
  rm -f "$IMG"
 
  OFFSET="$KERNEL_OFFS"
+ b_signelf "${PREFIX_PROG_STRIPPED}/$KERNEL_FILE"
  b_add2img "${PREFIX_PROG_STRIPPED}/$KERNEL_FILE" "$IMG"
 
  # Programs
  for prog in "${PROGS[@]}"; do
+ b_signelf "${PREFIX_PROG_STRIPPED}$prog"
  b_add2img "${PREFIX_PROG_STRIPPED}$prog" "$IMG"
  done
 }
@@ -286,10 +299,12 @@ b_dev_image() {
  # Kernel
  KERNEL_OFFS=$((KERNEL_OFFS - OFFS_USER_SCRIPT))
  OFFSET="$KERNEL_OFFS"
+ b_signelf "${PREFIX_PROG_STRIPPED}/$KERNEL_FILE"
  b_add2img "${PREFIX_PROG_STRIPPED}$KERNEL_FILE" "$PHOENIX_DEV_IMG"
 
  # Programs
  for prog in "${PROGS[@]}"; do
+ b_signelf "${PREFIX_PROG_STRIPPED}$prog"
  b_add2img "${PREFIX_PROG_STRIPPED}$prog" "$PHOENIX_DEV_IMG"
  done
 }