ARM: dts: am335x-pocketbeagle: enable pru

ARM: dts: am335x-pocketbeagle: enable pru

Now that the PRU code is upstream and can be loaded via remoteproc, adjust
the device tree to enable it and adjust the pin muxing so that the default
setting of the pins matches what's is given on the silkscreen and/or
pocketbeagle wiring.

Caveat:

In most cases, the silkscreen will indicate, for example, "PRU0.7",
but it doesn't indicate whether that pin should be enabled for input
or output. On the PRU a different MODE is used for input versus
output. So it is unclear which mode to enable (MODE5 = output, MODE6
= input). In cases where there is a choice (PRU1.11, PRU0.7, PRU0.4,
PRU0.1, PRU1.10, PRU0.6, PRU0.3, PRU0.2, and PRU0.5) output is assumed
(MODE5).

The remaining PRU silkscreen pins do not have a choice and are set as
follows:

PRU0.16  MODE5 input
PRU0.15i MODE6 input

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Message-ID: <20230822143051.7640-4-twoerner@gmail.com>
[tony@atomide.com: formatted description to fit 75 characters]
Signed-off-by: Tony Lindgren <tony@atomide.com>