[POWERPC] Enable CONFIG_FORCE_MAX_ZONEORDER for all PowerPC, and make selectable

This enables the FORCE_MAX_ZONEORDER Kconfig option for all PowerPC
systems.  Previously, it was enabled only for 64-bit systems.  We also
make the option selectable from the menu, so that the user can specify
different values.  This is useful for 32-bit systems that need to
allocate more than 4MB of physically contiguous memory.
Signed-off-by: NTimur Tabi <timur@freescale.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/Kconfig

@@ -211,14 +211,25 @@ source kernel/Kconfig.hz
 source kernel/Kconfig.preempt
 source "fs/Kconfig.binfmt"
 
-# We optimistically allocate largepages from the VM, so make the limit
-# large enough (16MB). This badly named config option is actually
-# max order + 1
 config FORCE_MAX_ZONEORDER
-	int
-	depends on PPC64
+	int "Maximum zone order"
 	default "9" if PPC_64K_PAGES
-	default "13"
+	default "13" if PPC64
+	default "11"
+	help
+	  The kernel memory allocator divides physically contiguous memory
+	  blocks into "zones", where each zone is a power of two number of
+	  pages.  This option selects the largest power of two that the kernel
+	  keeps in the memory allocator.  If you need to allocate very large
+	  blocks of physically contiguous memory, then you may need to
+	  increase this value.
+
+	  This config option is actually maximum order plus one. For example,
+	  a value of 11 means that the largest free memory block is 2^10 pages.
+
+	  The page size is not necessarily 4KB.  For example, on 64-bit
+	  systems, 64KB pages can be enabled via CONFIG_PPC_64K_PAGES.  Keep
+	  this in mind when choosing a value for this option.
 
 config HUGETLB_PAGE_SIZE_VARIABLE
 	bool