remoteproc: st_slim_rproc: add a slimcore rproc driver

remoteproc: st_slim_rproc: add a slimcore rproc driver

slim core is used as a basis for many IPs in the STi
chipsets such as fdma and demux. To avoid duplicating
the elf loading code in each device driver a slim
rproc driver has been created.

This driver is designed to be used by other device drivers
such as fdma, or demux whose IP is based around a slim core.
The device driver can call slim_rproc_alloc() to allocate
a slim rproc and slim_rproc_put() when finished.

This driver takes care of ioremapping the slim
registers (dmem, imem, slimcore, peripherals), whose offsets
and sizes can change between IP's. It also obtains and enables
any clocks used by the device. This approach avoids having
a double mapping of the registers as slim_rproc does not register
its own platform device. It also maps well to device tree
abstraction as it allows us to have one dt node for the whole
device.

All of the generic rproc elf loading code can be reused, and
we provide start() stop() hooks to start and stop the slim
core once the firmware has been loaded. This has been tested
successfully with fdma driver.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>