virtio-mmio: convert to devm_platform_ioremap_resource

[ Upstream commit c64eb62cfce242a57a7276ca8280ae0baab29d05 ]

Use devm_platform_ioremap_resource() to simplify code, which
contains platform_get_resource, devm_request_mem_region and
devm_ioremap.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Stable-dep-of: 55c91fedd03d ("virtio-mmio: don't break lifecycle of vm_dev")
Signed-off-by: Sasha Levin <sashal@kernel.org>