linux-ti-staging: Add dm-verity kernel config

Add a kernel config fragment enabling dm-verity and its crypto
dependencies (CONFIG_DM_VERITY, CONFIG_DM_CRYPT, CONFIG_BLK_DEV_DM).
Applied via KERNEL_CONFIG_FRAGMENTS, which setup-defconfig.inc reads
and merges directly through merge_config.sh.

Gated on DM_VERITY_IMAGE being set, matching the rest of the dm-verity
dynamic layer.

Signed-off-by: Atharv Dubey <a-dubey@ti.com>
Signed-off-by: Ryan Eatmon <reatmon@ti.com>

meta-ti-bsp/dynamic-layers/security-layer/recipes-kernel/linux/files/dm-verity.cfg

@@ -0,0 +1,5 @@
+CONFIG_MD=y
+CONFIG_BLK_DEV_DM=y
+CONFIG_DM_CRYPT=y
+CONFIG_DM_VERITY=y
+CONFIG_CRYPTO_SHA256=y

meta-ti-bsp/dynamic-layers/security-layer/recipes-kernel/linux/linux-ti-staging_%.bbappend

@@ -0,0 +1,5 @@
+# Enable the dm-verity kernel config fragment via KERNEL_CONFIG_FRAGMENTS.
+FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
+
+SRC_URI += "${@'file://dm-verity.cfg' if d.getVar('DM_VERITY_IMAGE') else ''}"
+KERNEL_CONFIG_FRAGMENTS += "${@'${UNPACKDIR}/dm-verity.cfg' if d.getVar('DM_VERITY_IMAGE') else ''}"