serial: 8250: pxa: Remove unneeded <linux/pm_runtime.h>

The 8250 PXA driver never used Runtime PM, so there was never a need to
include <linux/pm_runtime.h>.

Fixes: ab28f51c ("serial: rewrite pxa2xx-uart to use 8250_core")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/9fd96fba9bbbbdeb16af0dc07ae9dee21c8e297c.1651494971.git.geert+renesas@glider.be


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>