ARM: 8980/1: Allow either FLATMEM or SPARSEMEM on the multiplatform build

ARMv7 chips with LPAE can often benefit from SPARSEMEM, as portions of
system memory can be located deep in the 36-bit address space.  Allow
FLATMEM or SPARSEMEM to be selectable at compile time; FLATMEM remains
the default.

This is based on Kevin's "[PATCH 3/3] ARM: Allow either FLATMEM or
SPARSEMEM on the multi-v7 build" from [1] and shamelessly rips off his
commit message text above.  As Arnd pointed out at [2] there doesn't
seem to be any reason to tie this specifically to ARMv7, so this has
been changed to apply to all multiplatform kernels.

The addition of this option does not change the defaults and a build with
any defconfig will behave the same way as previously.

The only effect this change has is to enable user to change "Memory model"
selection in interactive kernel configuration (menuconfig, xconfig etc).

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-September/286837.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-October/298950.html

[ rppt: added ARCH_SELECT_MEMORY_MODEL and updated the changelog ]

Cc: Kevin Cernekee <cernekee@gmail.com>
Tested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/Kconfig

@@ -312,6 +312,9 @@ choice
 config ARCH_MULTIPLATFORM
 	bool "Allow multiple platforms to be selected"
 	depends on MMU
+	select ARCH_FLATMEM_ENABLE
+	select ARCH_SPARSEMEM_ENABLE
+	select ARCH_SELECT_MEMORY_MODEL
 	select ARM_HAS_SG_CHAIN
 	select ARM_PATCH_PHYS_VIRT
 	select AUTO_ZRELADDR
@@ -1515,9 +1518,15 @@ config OABI_COMPAT
 config ARCH_HAS_HOLES_MEMORYMODEL
 	bool
 
+config ARCH_SELECT_MEMORY_MODEL
+	bool
+
+config ARCH_FLATMEM_ENABLE
+	bool
+
 config ARCH_SPARSEMEM_ENABLE
 	bool
-	select SPARSEMEM_STATIC
+	select SPARSEMEM_STATIC if SPARSEMEM
 
 config HAVE_ARCH_PFN_VALID
 	def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM