ARM: shmobile: r8a7740: Multiplatform support

Enable r8a7740 Multiplatform support for the generic r8a7740
machine vector. No board support is enabled, and the board
code for Armadillo 800 EVA DT Reference is left by itself.

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