Update the list of available IMAGE_FEATURES with the sub-features of
'debug-tweaks' and add 'splash'.
(From OE-Core rev: 1e46220bb3901476266846447ff40533c9bffa1d)
Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>