CONFIG_OF_OVERLAY: enable for aarch64 and powerpc

CONFIG_OF_OVERLAY is now selected by some KUnit tests where CONFIG_OF is enabled. Because these tests are enabled for aarch64 and powerpc we also need to enable CONFIG_OF_OVERLAY for these arches.

See: 5776526b ('clk: Add KUnit tests for clk fixed rate basic type')
274aff87 ('clk: Add KUnit tests for clks registered with struct clk_parent_data')
5c9dd72d (of: Add a KUnit test for overlays and test managed APIs)

Signed-off-by: Scott Weaver scweaver@redhat.com