kconfig check: require BLK_DEV_INITRD

Always needed for the initramfs, so let's enforce it.

See also: https://gitlab.com/postmarketOS/pmaports/issues/237

pmb/config/__init__.py

@@ -170,6 +170,7 @@ build_cross_native = ["linux-*", "arch-bin-masquerade", "u-boot*"]
 necessary_kconfig_options = {
     "all": {
         "ANDROID_PARANOID_NETWORK": False,
+        "BLK_DEV_INITRD": True,
         "DEVTMPFS": True,
         "DM_CRYPT": True,
         "EXT4_FS": True,