serial: qcom_geni_serial: use DT aliases according to DT bindings

Device tree bindings do not specify "hsuart" aliases, instead all serial
ports should use "serial" alias name as noted by Rob Herring [1].
Make qcom_geni_serial driver use "serial" alias and fallback to "hsuart"
if one is not found.

[1] https://lore.kernel.org/linux-arm-msm/6dd1f5cd-03c7-5945-9fa2-1c2698405110@linaro.org/

Cc: Rob Herring <robh+dt@kernel.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210621211528.1607516-1-dmitry.baryshkov@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>