remoteproc: pru: Add pru-specific debugfs support

The remoteproc core creates certain standard debugfs entries,
that does not give a whole lot of useful information for the
PRUs. The PRU remoteproc driver is enhanced to add additional
debugfs entries for PRU. These will be auto-cleaned up when
the parent rproc debug directory is removed.

The enhanced debugfs support adds two new entries: 'regs' and
'single_step'. The 'regs' dumps out the useful CTRL sub-module
registers as well as each of the 32 GPREGs and CT_REGs registers.
The GPREGs and CT_REGs though are printed only when the PRU is
halted and accessible as per the IP design.

The 'single_step' utilizes the single-step execution of the PRU
cores. Writing a non-zero value performs a single step, and a
zero value restores the PRU to execute in the same mode as the
mode before the first single step. (note: if the PRU is halted
because of a halt instruction, then no change occurs).

Logic for setting the PC and jumping over a halt instruction shall
be added in the future.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20201208141002.17777-5-grzegorz.jaszczyk@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>