sh: Merge legacy and dynamic PMB modes.

This implements a bit of rework for the PMB code, which permits us to
kill off the legacy PMB mode completely. Rather than trusting the boot
loader to do the right thing, we do a quick verification of the PMB
contents to determine whether to have the kernel setup the initial
mappings or whether it needs to mangle them later on instead.

If we're booting from legacy mappings, the kernel will now take control
of them and make them match the kernel's initial mapping configuration.
This is accomplished by breaking the initialization phase out in to
multiple steps: synchronization, merging, and resizing. With the recent
rework, the synchronization code establishes page links for compound
mappings already, so we build on top of this for promoting mappings and
reclaiming unused slots.

At the same time, the changes introduced for the uncached helpers also
permit us to dynamically resize the uncached mapping without any
particular headaches. The smallest page size is more than sufficient for
mapping all of kernel text, and as we're careful not to jump to any far
off locations in the setup code the mapping can safely be resized
regardless of whether we are executing from it or not.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/mm/Kconfig

@@ -91,16 +91,6 @@ config PMB
 	  32-bits through the SH-4A PMB. If this is not set, legacy
 	  29-bit physical addressing will be used.
 
-config PMB_LEGACY
-	bool "Support legacy boot mappings for PMB"
-	depends on PMB
-	select 32BIT
-	help
-	  If this option is enabled, fixed PMB mappings are inherited
-	  from the boot loader, and the kernel does not attempt dynamic
-	  management. This is the closest to legacy 29-bit physical mode,
-	  and allows systems to support up to 512MiB of system memory.
-
 config X2TLB
 	def_bool y
 	depends on (CPU_SHX2 || CPU_SHX3) && MMU