staging: android/ram_console: Don't build on arches w/o ioremap

This patch fixes UML build:

    CC      drivers/staging/android/ram_console.o
  drivers/staging/android/ram_console.c: In function
  'ram_console_driver_probe':
  drivers/staging/android/ram_console.c:358:2: error: implicit declaration
  of function 'ioremap' [-Werror=implicit-function-declaration]
  cc1: some warnings being treated as errors
  make[3]: *** [drivers/staging/android/ram_console.o] Error 1

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: Ida6353dc566792ed184281e8cb24e76514959dbb