sm8x50-userdebug: Add a generic build target for Qcom ARMv9 devboards

Adding a 64-bit only generic build target for Qcom armv9
(Snapdragon 8 gen) devboards and enable it in LKFT. It is
supported only on v6.8+ kernel versions.

SM8550-HDK, https://www.lantronix.com/products/snapdragon-8-gen-2-mobile-hardware-development-kit/
is the primary device supported by this build configuration.
Other Snapdragon 8 gen devboards are supported on the best
efforts basis.

Smoke tested sm8x50-userdebug build target on SM8550-HDK.
Boots to UI with upstream kernel using software rendering
and linux-firmware binaries for now, which is good enough to
kickstart testing in LKFT lab.

`lunch` target is not added yet and will be added as soon
the firmware binaries land in linaro-vendor / linux-firmware
repo to make sure that the device has more features enabled
and is in a more usable state. Boot image header v2 is used
for now, while we are working on releasing ABL with header
v4 support.

And since qcom,board-id and qcom,msm-id DT properties are no
longer accepted upstream, we are using fdtoverlay to apply
them at build time. So make sure that the base DT is built
with `DTC_FLAGS=-@` build flag to allow overlays, otherwise
fdtoverlay command will run into "FDT_ERR_NOTFOUND" error at
the build time.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: I2c6a0331173ef11a542b07ee3a270ece36d96786
15 files changed