arm64: dts: qcom: msm8916/39: Fix venus memory size

arm64: dts: qcom: msm8916/39: Fix venus memory size

Both MSM8916 and MSM8939 have unnecessarily large reservations for the
venus firmware for some reason. According to the ELF headers and
downstream [1] 5 MiB is enough. Let's set the minimum size as default.

With the dynamic reserved memory allocations boards can easily override
this if needed, although in practice there does not seem to be any
device with a different venus firmware size.

[1]: https://git.codelinaro.org/clo/la/kernel/msm-3.10/-/blame/LA.BR.1.2.9.1-02310-8x16.0/arch/arm/boot/dts/qcom/msm8939-common.dtsi#L69

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20230911-msm8916-rmem-v1-9-b7089ec3e3a1@gerhold.net
Signed-off-by: Bjorn Andersson <andersson@kernel.org>