arm64: dts: qcom: rename pm8450a dtsi to sa8540p-pmics

pm8450a.dtsi was introduced for the descriptions of pmics used on
sa8540p based boards. Rename the dtsi to make this relationship
explicit.

Signed-off-by: Eric Chanudet <echanude@redhat.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Tested-by: Andrew Halaney <ahalaney@redhat.com> # sa8540p-ride
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221219191000.2570545-2-echanude@redhat.com