ARM: mach-stmp378x: remove mach

ARM: mach-stmp378x: remove mach

This mach has not seen any updates since the initial inclusion besides
generic cleanup. Furthermore:

- The i.MX23 covered in mach-mxs is just a renamed version of the
  STMP378x.

- mach-stmp378x has a lot of reinvented interfaces, leaking all sorts of
  mach-related includes into the drivers. One example is the dmaengine
  which does not use the linux dmaengine-API but some privately exported
  symbols. So drivers cannot be reused. mach-mxs does it better.

- There is only one board defined (which I couldn't find any trace of
  despite being a development board). It has been converted to
  mach-mxs in a previous patch.

Since the only user of this mach was converted, it means that
mach-stmp378x can go.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>