mm/damon/tests: add .kunitconfig file for DAMON kunit tests

'--kunitconfig' option of 'kunit.py run' supports '.kunitconfig' file name
convention.  Add the file for DAMON kunit tests for more convenient kunit
run.

Link: https://lkml.kernel.org/r/20240827030336.7930-10-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Gow <davidgow@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/tests/.kunitconfig

+# for DAMON core
+CONFIG_KUNIT=y
+CONFIG_DAMON=y
+CONFIG_DAMON_KUNIT_TEST=y
+
+# for DAMON vaddr ops
+CONFIG_MMU=y
+CONFIG_PAGE_IDLE_FLAG=y
+CONFIG_DAMON_VADDR=y
+CONFIG_DAMON_VADDR_KUNIT_TEST=y
+
+# for DAMON sysfs interface
+CONFIG_SYSFS=y
+CONFIG_DAMON_SYSFS=y
+CONFIG_DAMON_SYSFS_KUNIT_TEST=y
+
+# for DAMON debugfs interface
+CONFIG_DEBUG_FS=y
+CONFIG_DAMON_PADDR=y
+CONFIG_DAMON_DBGFS_DEPRECATED=y
+CONFIG_DAMON_DBGFS=y
+CONFIG_DAMON_DBGFS_KUNIT_TEST=y