arm: Finish migration of CONFIG_MACH_TYPE

As this is only useful when booting with ATAGs, which are now largely
disabled, remove this value for the remaining platforms.  We have a few
places in the code that had been testing for MACH_TYPE as a sort of
internal logic.  Update those to use different but still correct CONFIG
symbols.

Cc: Phil Sutter <phil@nwl.cc>
Signed-off-by: Tom Rini <trini@konsulko.com>

README

@@ -586,16 +586,6 @@ The following options need to be configured:
 		crash. This is needed for buggy hardware (uc101) where
 		no pull down resistor is connected to the signal IDE5V_DD7.
 
-		CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]
-
-		This setting is mandatory for all boards that have only one
-		machine type and must be used to specify the machine type
-		number as it appears in the ARM machine registry
-		(see https://www.arm.linux.org.uk/developer/machines/).
-		Only boards that have multiple machine types supported
-		in a single configuration file and the machine type is
-		runtime discoverable, do not have to use this setting.
-
 - vxWorks boot parameters:
 
 		bootvx constructs a valid bootline using the following