generic: add ioremap_wc() interface wrapper

x86 has ioremap_wc for wc remap. Also introduce a generic ioremap_wc
aliased to ioremap_uc so that drivers can use this interface transparently.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>