remoteproc/omap: Request a timer(s) for remoteproc usage

The remote processors in OMAP4+ SoCs are equipped with internal
timers, like the internal SysTick timer in a Cortex M3/M4 NVIC or
the CTM timer within Unicache in IPU & DSP. However, these timers
are gated when the processor subsystem clock is gated, making
them rather difficult to use as OS tick sources. They will not
be able to wakeup the processor from any processor-sleep induced
clock-gating states.

This can be avoided by using an external timer as the tick source,
which can be controlled independently by the OMAP remoteproc
driver code, but still allowing the processor subsystem clock to
be auto-gated when the remoteproc cores are idle.

This patch adds the support for OMAP remote processors to request
timer(s) to be used by the remoteproc. The timers are enabled and
disabled in line with the enabling/disabling of the remoteproc.
The timer data is not mandatory if the advanced device management
features are not required.

The core timer functionality is provided by the OMAP DMTimer
clocksource driver, which does not export any API. The logic is
implemented through the timer device's platform data ops. The OMAP
remoteproc driver mainly requires ops to request/free a dmtimer,
and to start/stop a timer. The split ops helps in controlling the
timer state without having to request and release a timer everytime
it needs to use the timer.

NOTE: If the gptimer is already in use by the time IPU and/or
DSP are loaded, the processors will fail to boot.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Andrew F. Davis <afd@ti.com>
Acked-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200324110035.29907-11-t-kristo@ti.com
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

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