defconfig: 8994: Enable MSM8992 support

MSM8992 and MSM8994 can be supported in a single-binary
configuration, so enable MSM8992 support in the 8994
defconfig.

Change-Id: I23c0f9b0d86c82d090888099a69b0b4fcc773583
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>