firmware: arm_scmi: Remove const from transport descriptors

The descriptor structure scmi_desc contains a variety of fields related to
the transport functionalities and it is defined by the transport drivers
themselves; such elements, though, serve varied purposes and have different
lifetime.

In particular, while there are some of those elements that provide a
description of transport features that are supposed to be immutable, on
the other side there are present also some other characteristics that are
instead supposed to be configurable on a per-platform base since they
represent configuration features tied to the specific hardware/firmware
system.

The immutable fields are already qualified as const on the their own; get
rid of the structure-level const qualifier which is not needed, so as to
enable possible runtime customization of the mutable configuration
features.

No functional change.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Peng Fan <peng.fan@nxp.com>  #i.MX95 19x19 EVK
Message-Id: <20240730144707.1647025-2-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>