arch/Kconfig: split PAGE_SIZE_LESS_THAN_256KB from PAGE_SIZE_LESS_THAN_64KB

Patch series "Fix CONFIG_TEST_KMOD with 256kB page size".

The kernel test robot reported a build error [1] from a failed assertion
in fs/btrfs/inode.c with a hexagon randconfig that includes
CONFIG_PAGE_SIZE_256KB.  This error is the same one that was addressed
by commit b05fbcc3 ("btrfs: disable build on platforms having page
size 256K") but CONFIG_TEST_KMOD selects CONFIG_BTRFS without having the
"page size less than 256kB dependency", which results in the error
reappearing.

The first patch introduces CONFIG_PAGE_SIZE_LESS_THAN_256KB by splitting
it off from CONFIG_PAGE_SIZE_LESS_THAN_64KB, which was introduced in
commit 1f0e290c ("arch: Add generic Kconfig option indicating page
size smaller than 64k") for a similar reason in 5.16-rc3.

The second patch uses that configuration option for CONFIG_BTRFS to
reduce duplication.

The third patch resolves the build error by adding
CONFIG_PAGE_SIZE_LESS_THAN_256KB as a dependency to CONFIG_TEST_KMOD so
that CONFIG_BTRFS does not get enabled under that invalid configuration.

[1]: https://lore.kernel.org/r/202111270255.UYOoN5VN-lkp@intel.com/

This patch (of 3):

btrfs requires a page size smaller than 256kB.  To use that dependency
in other places, introduce CONFIG_PAGE_SIZE_LESS_THAN_256KB and reuse
that dependency in CONFIG_PAGE_SIZE_LESS_THAN_64KB.

Link: https://lkml.kernel.org/r/20211129230141.228085-1-nathan@kernel.org
Link: https://lkml.kernel.org/r/20211129230141.228085-2-nathan@kernel.orgSigned-off-by: Nathan Chancellor <nathan@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/Kconfig

@@ -998,6 +998,10 @@ config PAGE_SIZE_LESS_THAN_64KB
 	depends on !PAGE_SIZE_64KB
 	depends on !PARISC_PAGE_SIZE_64KB
 	depends on !PPC_64K_PAGES
+	depends on PAGE_SIZE_LESS_THAN_256KB
+
+config PAGE_SIZE_LESS_THAN_256KB
+	def_bool y
 	depends on !PPC_256K_PAGES
 	depends on !PAGE_SIZE_256KB