lib/Kconfig.debug: make TEST_KMOD depend on PAGE_SIZE_LESS_THAN_256KB

Commit b05fbcc ("btrfs: disable build on platforms having page size
256K") disabled btrfs for configurations that used a 256kB page size.
However, it did not fully solve the problem because CONFIG_TEST_KMOD
selects CONFIG_BTRFS, which does not account for the dependency.  This
results in a Kconfig warning and the failed BUILD_BUG_ON error
returning.

  WARNING: unmet direct dependencies detected for BTRFS_FS
    Depends on [n]: BLOCK [=y] && !PPC_256K_PAGES && !PAGE_SIZE_256KB [=y]
    Selected by [m]:
    - TEST_KMOD [=m] && RUNTIME_TESTING_MENU [=y] && m && MODULES [=y] && NETDEVICES [=y] && NET_CORE [=y] && INET [=y] && BLOCK [=y]

To resolve this, add CONFIG_PAGE_SIZE_LESS_THAN_256KB as a dependency of
CONFIG_TEST_KMOD so there is no more invalid configuration or build
errors.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: b05fbcc ("btrfs: disable build on platforms having page size 256K")
Signed-off-by: Nathan Chancellor <[email protected]>
Reported-by: kernel test robot <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: David Sterba <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Luis Chamberlain <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: nathanchance

lib/Kconfig.debug

@@ -2505,6 +2505,7 @@ config TEST_KMOD
 	depends on m
 	depends on NETDEVICES && NET_CORE && INET # for TUN
 	depends on BLOCK
+	depends on PAGE_SIZE_LESS_THAN_256KB # for BTRFS
 	select TEST_LKM
 	select XFS_FS
 	select TUN