activation: Create ubi write function

Move the code that creates the ubi volumes into a separate
write flash function to make it easier to implement
different flash write functions for other flash layouts.

To implement a different write flash function:

1. Modify the Makefile.am file to include the desired code
location. Ex:
  if UBI
    include ubi/Makefile.am.include
  else
    include <other>/Makefile.am.include
2. Implement the Activation::flashWrite in <other>/flash.cpp

Tested: Verified code update still worked.

Change-Id: Ide4d135695dad27e0dc1b5a776a276dfb2ca9aa6
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/ubi/Makefile.am.include b/ubi/Makefile.am.include
new file mode 100644
index 0000000..7bcfcb2
--- /dev/null
+++ b/ubi/Makefile.am.include
@@ -0,0 +1,2 @@
+phosphor_image_updater_SOURCES += \
+	%reldir%/flash.cpp