arm64: dts: qcom: x1e80100: Add UART2

GENI SE2 within QUP0 is used as UART on some devices, describe it.
While at it, rewrite the adjacent UART21 pins node to make it more
easily modifiable.

Signed-off-by: Konrad Dybcio <quic_kdybcio@quicinc.com>
Link: https://lore.kernel.org/r/20240826-topic-sl7-v2-4-c32ebae78789@quicinc.com


Signed-off-by: Bjorn Andersson <andersson@kernel.org>