cmd: ti: pd: Add debug command for K3 power domains

Add support command for debugging K3 power domains. This is useful with
the HSM rearch setup, where power domains are directly controlled by SPL
instead of going through the TI SCI layer. The debugging support is only
available in the u-boot codebase though, so the raw register access
power domain layer must be enabled on u-boot side for this to work. By
default, u-boot side uses the TI SCI layer, and R5 SPL only uses the
direct access methods.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tero Kristo <kristo@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>