meta-facebook: add secondary-emmc feature

  * Define a MACHINE_FEATURE that enables a secondary eMMC device.
  * Add kernel and base-files support for mounting the eMMC device
    using btrfs.
  * Enable machine feature for Bletchley.

Signed-off-by: Potin Lai <potin.lai@quantatw.com>
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3fde3b285720c137c4e5bbbad233e4ef40b84d54
diff --git a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
index 1d1a5b8..3d0e7aa 100644
--- a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
+++ b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
@@ -10,6 +10,7 @@
 require conf/machine/include/ast2600.inc
 require conf/machine/include/obmc-bsp-common.inc
 require conf/machine/include/facebook-tpm2.inc
+require conf/machine/include/facebook-secondary-emmc.inc
 
 FLASH_SIZE = "131072"