generic: add phys_addr_t for holding physical addresses

Add a kernel-wide "phys_addr_t" which is guaranteed to be able to hold
any physical address.  By default it equals the word size of the
architecture, but a 32-bit architecture can set ARCH_PHYS_ADDR_T_64BIT
if it needs a 64-bit phys_addr_t.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/mm/Kconfig b/mm/Kconfig
index 0bd9c2d..91ee392 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -187,6 +187,9 @@
 	help
 	  This option allows memory and IO resources to be 64 bit.
 
+config PHYS_ADDR_T_64BIT
+	def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
+
 config ZONE_DMA_FLAG
 	int
 	default "0" if !ZONE_DMA