arm64: dts: qcom: milos: Reduce rmtfs_mem size to 2.5MiB

arm64: dts: qcom: milos: Reduce rmtfs_mem size to 2.5MiB

The rmtfs_mem region is currently sized at 6MiB but the default for
milos downstream is 2.5MiB. This causes remoteproc crashes on devices
that expect the smaller size:

modem_ac.c:281:Access Control Error: Could not protect the region specified:Start:e1f00000 End:e2180000, PID:1

Reduce the default to 2.5MiB to match the QCOM downstream config, and
override the size for FP6.

Fixes: d9d59d105f98 ("arm64: dts: qcom: Add initial Milos dtsi")
Reviewed-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Signed-off-by: Alexander Koskovich <akoskovich@pm.me>
Link: https://lore.kernel.org/r/20260323-asteroids-v2-1-1a35fa9e178a@pm.me
Signed-off-by: Bjorn Andersson <andersson@kernel.org>