ARM: shmobile: Remove AP4EVB board support

Remove board support for the sh7372 based AP4EVB board

The sh7372 SoC support code is still kept around since it
is in use by the Mackerel board which is basically a more
recent board where the design is based on AP4EVB.

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