remoteproc: core: transform struct fw_rsc_vdev_vring reserved field in pa

In current implementation, struct fw_rsc_vdev_vring which describes
vring resource in firmware resource table owns only device address,
because it assumes that host is responsible of vring allocation and
only device address is needed by coprocessor.
But if vrings need to be fixed in system memory map for any reasons
(security, SoC charactieristics...), physical address is needed exatly
identified the memory chunck by host.

For that let's transform reserved field of struct fw_rsc_vdev_vring
to pa (physical address).

Signed-off-by: Loic Pallardy <loic.pallardy@st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>