[display] Add blanking pause allowed -policy. JB#41340
[display] Add blanking pause allowed -policy. JB#41340

The rules for allowing / ending blanking pause are scattered
around display plugin.

Combine the logic into one evaluation function.

Signed-off-by: Simo Piiroinen <6d5e5360bed3d486f7d9fb26b0f737f7d4fd45ee@jollamobile.com>

spiiroin/mce,spiiroin/mce,spiiroin/mce,spiiroin/mce