MIPS: Define ioremap_uc

All architectures must now define ioremap_uc(), but MIPS currently
only has ioremap_nocache().

Fixes: 4c73e892 ("arch/*/io.h: Add ioremap_uc() to all architectures")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11263/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>