ARM: mach-shmobile: ap4evb, mackerel: fixup scif initialisation for zboot

* Set receive enable and transmit enable bits of SCASCR0 (E6C400089).
  Values previously written to this register was bogus.

  Curiously earlyprintk works with the previous code.

* Remove duplicate initialisation of GPIO port 152, SCIFA0_TXD (0xE6053098).
  This should have no effect other than to very slightly reduce the amount of
  code.

Reported-by: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>