MIPS: Limit fixrange_init() to the FIXMAP region

fixrange_init() allocates page tables for all addresses higher than
FIXADDR_TOP.  On processors that override the default FIXADDR_TOP
address of 0xfffe_0000, this can consume up to 4 pages (1 page per 4MB)
for pgd's that are never used.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/1980/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/pgtable-64.c

@@ -76,5 +76,5 @@ void __init pagetable_init(void)
 	 * Fixed mappings:
 	 */
 	vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;
-	fixrange_init(vaddr, 0, pgd_base);
+	fixrange_init(vaddr, vaddr + FIXADDR_SIZE, pgd_base);
 }