serial: lpc32xx_hs: allow compile-testing

The only thing that prevents building this driver on other
platforms is the mach/hardware.h include, which is not actually
used here at all, so remove the line and allow CONFIG_COMPILE_TEST.

Link: https://lore.kernel.org/r/20190809144043.476786-5-arnd@arndb.de


Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>