[ARM] Fix non-page aligned boot time mappings

AT91SAM9260 stopped booting with the recent changes to MM
initialisation - it was asking for a non-aligned virtual address
which caused loops to be non-terminal.  Fix this by rounding
virtual addresses down, but remember to include the offset in
the length, and round the length up to the following page.

This means that asking for a mapping of 4K starting at 2K into
a page maps two pages as one would expect.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/mmu.c

@@ -527,9 +527,9 @@ void __init create_mapping(struct map_desc *md)
 		return;
 	}
 
-	addr = md->virtual;
+	addr = md->virtual & PAGE_MASK;
 	phys = (unsigned long)__pfn_to_phys(md->pfn);
-	length = PAGE_ALIGN(md->length);
+	length = PAGE_ALIGN(md->length + (md->virtual & ~PAGE_MASK));
 
 	if (type->prot_l1 == 0 && ((addr | phys | length) & ~SECTION_MASK)) {
 		printk(KERN_WARNING "BUG: map for 0x%08lx at 0x%08lx can not "