drm/i915: Unset reset pch handshake when PCH is not present in one place

Right now RESET_PCH_HANDSHAKE_ENABLE is enabled all the times inside
of intel_power_domains_init_hw() and if PCH is NOP it is unsed in
i915_gem_init_hw().
So making skl_pch_reset_handshake() handle both cases and calling
it for the missing gens in intel_power_domains_init_hw().
Ivybridge have a different register and bits but with the same
objective so moving it too.

v2(Rodrigo):
- handling IVYBRIDGE case inside intel_pch_reset_handshake()

v4(Rodrigo and Ville):
- moving the enable/disable decision to callers

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180918204714.27306-2-jose.souza@intel.com