firmware: arm_scmi: Support 'reg-io-width' property for shared memory

firmware: arm_scmi: Support 'reg-io-width' property for shared memory

Some shared memory areas might only support a certain access width,
such as 32-bit, which memcpy_{from,to}_io() does not adhere to at least
on ARM64 by making both 8-bit and 64-bit accesses to such memory.

Update the shmem layer to support reading from and writing to such
shared memory area using the specified I/O width in the Device Tree. The
various transport layers making use of the shmem.c code are updated
accordingly to pass the I/O accessors that they store.

Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Message-Id: <20240827182450.3608307-3-florian.fainelli@broadcom.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>