soc: qcom: apr: make code more reuseable

APR and other packet routers like GPR are pretty much same and
interact with other drivers in similar way.

Ex: GPR ports can be considered as APR services, only difference
is they are allocated dynamically.

Other difference is packet layout, which should not matter
with the apis abstracted. Apart from this the rest of the
functionality is pretty much identical across APR and GPR.

Make the apr code more reusable by abstracting it service level,
rather than device level so that we do not need to write
new drivers for other new packet routers like GPR.

This patch is in preparation to add GPR support to this driver.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210927135559.738-4-srinivas.kandagatla@linaro.org