PM / Domains: Restore alignment of slaves in debugfs output

The slave domains are no longer aligned with the table header in the
/sys/kernel/debug/pm_genpd/pm_genpd_summary output. Worse, the alignment
differs depending on the actual name of the state.

Format the state name and index into a buffer, and print that like
before to restore alignment.

Use "%u" for unsigned int while we're at it.

Fixes: fc5cbf0c (PM / Domains: Support for multiple states)
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>