ARM: shmobile: Remove Bonito board support

Remove board support for the r8a7740 based Bonito board

The r8a7740 SoC support code is still kept around since it
is in use by the Armadillo800eva board which is basically a more
recent board where the design is based on Bonito.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>