version: Separate our version string from the version command

In order to be able to disable all commands we need to construct our
version string in a common file, and have the version command reference
that string, like the other users of it do.  Create common/version.c
with just the strings.

Signed-off-by: Tom Rini <trini@konsulko.com>

common/Makefile

@@ -10,6 +10,7 @@ obj-y += main.o
 obj-y += exports.o
 obj-$(CONFIG_HUSH_PARSER) += cli_hush.o
 obj-$(CONFIG_AUTOBOOT) += autoboot.o
+obj-y += version.o
 
 # # boards
 obj-y += board_f.o