remoteproc: mtk_scp: Reorder scp_probe() sequence

remoteproc: mtk_scp: Reorder scp_probe() sequence

Cleanup the scp_probe() function by reordering some calls in this
function, useful to reduce the usage of goto(s), and preparing
for one more usage of dev_err_probe().

In particular, we can get the clocks before mapping the memory region,
and move the mutexes initialization right before registering the ipi
handler (which is the first mutex user in this driver).

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220124120915.41292-2-angelogioacchino.delregno@collabora.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>