arm64: dts: qcom: ipq6018: Remove unused 'qcom,config-pipe-trust-reg' property

'qcom,config-pipe-trust-reg' property doesn't seem to be
used by the qcom, bam_dma driver, so remove the same
from 'ipq6018' dts.

This is a preparatory patch for subsequent patch in
this series which converts the qcom_bam_dma device-tree
binding into YAML format.

Without this change, 'make dtbs_check' leads to the following
error:
 $ arch/arm64/boot/dts/qcom/ipq6018-cp01-c1.dt.yaml:
     dma-controller@704000: 'qcom,config-pipe-trust-reg' does not match
     any of the regexes: 'pinctrl-[0-9]+'

Fix the same.

Cc: Thara Gopinath <thara.gopinath@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211013105541.68045-3-bhupesh.sharma@linaro.org