serial: clps711x: Remove board support

Since board support for the CLPS711X platform was removed
(commit 4a56f46a ("ARM: clps711x: Remove boards support")),
remove the board support from the driver.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>