msm: ep_pcie: Changes to avoid handle_perst_wq schedule out

Queue handle_perst_wq as system_highpri_wq to avoid WQ getting
scheduled out.

Change-Id: I28fdc6e3d51b98b132c04bf552c40c9dad3cbd0f
Signed-off-by: Subramanian Ananthanarayanan <skananth@codeaurora.org>
Signed-off-by: Gauri Joshi <gaurjosh@codeaurora.org>