ARM: shmobile: Add defconfig for shmobile multiplatform

This is intended to be a base for a defconfig to cover all
shmobile multiplatform boards. It currently includes configuration
for the following boards:

* KZM9D
* Lager
* Koelsch

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Magnus Damm <damm@opensource.se>