ipq40xx: only include ath10k-board-qca4019 for the generic subtarget

Since MikroTik subtarget now uses dynamic BDF loading its crucial that it
doesnt include the board-2.bin at all which is provided by the
ath10k-board-qca4019 package.

So to resolve this include the ath10k-board-qca4019 package only for the
generic subtarget via its Makefile instead of via the target Makefile.

Signed-off-by: Robert Marko <robimarko@gmail.com>