mtd: physmap_of: Add non-obsolete map_rom probe

Previously, the only way to map a NOR device as a simple ROM was to
use the obsolete "direct-mapped" compatible binding (which further
requires device_type = "nor" and probe-type = "NOR" properties).

This patch adds an "mtd-rom" compatible binding to the "map_rom"
probe type.
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

Documentation/devicetree/bindings/mtd/mtd-physmap.txt

@@ -4,8 +4,8 @@ Flash chips (Memory Technology Devices) are often used for solid state
 file systems on embedded devices.
 
  - compatible : should contain the specific model of mtd chip(s)
-   used, if known, followed by either "cfi-flash", "jedec-flash"
-   or "mtd-ram".
+   used, if known, followed by either "cfi-flash", "jedec-flash",
+   "mtd-ram" or "mtd-rom".
  - reg : Address range(s) of the mtd chip(s)
    It's possible to (optionally) define multiple "reg" tuples so that
    non-identical chips can be described in one node.

drivers/mtd/maps/physmap_of.c

@@ -339,6 +339,10 @@ static struct of_device_id of_flash_match[] = {
 		.compatible     = "mtd-ram",
 		.data           = (void *)"map_ram",
 	},
+	{
+		.compatible     = "mtd-rom",
+		.data           = (void *)"map_rom",
+	},
 	{
 		.type		= "rom",
 		.compatible	= "direct-mapped"