Revert "MIPS: page.h: Provide more readable definition for PAGE_MASK."

This reverts commit c17a655.

Manuel Lauss writes:

lmo commit c17a655 (MIPS: page.h: Provide more readable definition for
PAGE_MASK) apparently breaks ioremap of 36-bit addresses on my Alchemy
systems (PCI and PCMCIA) The reason is that in arch/mips/mm/ioremap.c
line 157  (phys_addr &= PAGE_MASK) bits 32-35 are cut off.  Seems the
new PAGE_MASK is explicitly 32bit, or one could make it signed instead
of unsigned long.

arch/mips/include/asm/page.h

@@ -31,7 +31,7 @@
 #define PAGE_SHIFT	16
 #endif
 #define PAGE_SIZE	(_AC(1,UL) << PAGE_SHIFT)
-#define PAGE_MASK	(~(PAGE_SIZE - 1))
+#define PAGE_MASK	(~((1 << PAGE_SHIFT) - 1))
 
 #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 #define HPAGE_SHIFT	(PAGE_SHIFT + PAGE_SHIFT - 3)