ARM: shmobile: Remove G4EVM machine support

This machine is using old CPU of shmobile (sh7377) and cannot obtain
machine, either.
Therefore, remove G4EVM support.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Simon Horman <horms@verge.net.au>