[MIPS] Always use virt_to_phys() when translating kernel addresses

This patch fixes two places where we used plain 'x - PAGE_OFFSET' to
achieve virtual to physical address convertions. This type of convertion
is no more allowed since commit 6f284a2ce7b8bc49cb8455b1763357897a899abb.

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>

[Build fixes for machines that don't use the generic dma-coherence.h]

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/pgtable.h b/include/asm-mips/pgtable.h
index 3fcfd79..0d3295f 100644
--- a/include/asm-mips/pgtable.h
+++ b/include/asm-mips/pgtable.h
@@ -75,7 +75,7 @@
  * Conversion functions: convert a page and protection to a page entry,
  * and a page entry and page directory to the page they refer to.
  */
-#define pmd_phys(pmd)		(pmd_val(pmd) - PAGE_OFFSET)
+#define pmd_phys(pmd)		virt_to_phys((void *)pmd_val(pmd))
 #define pmd_page(pmd)		(pfn_to_page(pmd_phys(pmd) >> PAGE_SHIFT))
 #define pmd_page_vaddr(pmd)	pmd_val(pmd)