drm/i915/vbt: Parse and use the new field with PSR2 TP2/3 wakeup time

A new field with the training pattern(TP) wakeup time for PSR2 was
added to VBT, so lets use it when available otherwise it will
fallback to PSR1 wakeup time.

v2: replacing enum to numerical usec time (Jani)

BSpec: 20131

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190312195743.8829-1-jose.souza@intel.com