[ARM] Cleanup arch/arm/mm a little

Move top_pmd into arch/arm/mm/mm.h - nothing outside arch/arm/mm
references it.

Move the repeated definition of TOP_PTE into mm/mm.h, as well as
a few function prototypes.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/mm.h

@@ -0,0 +1,19 @@
+/* the upper-most page table pointer */
+extern pmd_t *top_pmd;
+
+#define TOP_PTE(x)	pte_offset_kernel(top_pmd, x)
+
+static inline pmd_t *pmd_off(pgd_t *pgd, unsigned long virt)
+{
+	return pmd_offset(pgd, virt);
+}
+
+static inline pmd_t *pmd_off_k(unsigned long virt)
+{
+	return pmd_off(pgd_offset_k(virt), virt);
+}
+
+struct map_desc;
+
+void __init build_mem_type_table(void);
+void __init create_mapping(struct map_desc *md);