ipq807x: rename target to qualcommax

ipq807x: rename target to qualcommax

Currently, ipq807x only covers Qualcomm IPQ807x SoC-s.
However, Qualcomm also has IPQ60xx and IPQ50xx SoC-s under the AX WiSoC-s
and they share a lot of stuff with IPQ807x, especially IPQ60xx so to avoid
duplicating kernel patches and everything lets make a common target with
per SoC subtargets.

Start doing that by renaming ipq807x to qualcommax so that dependencies
on ipq807x target can be updated.

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