serial: xuartps: Enable clocks in the pm disable case also

When Power management is disabled then the clocks are not getting
enabled. This patch enables it for the !PM case also.
While at it also pm_runtime_set_active is called before
calling pm_runtime_enable.

Reported-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>