common:Add pronto_wlan for user variant builds

Add pronto_wlan into to common.mk. This change is needed
to build wlan driver for User variant builds.

Change-Id: Id20fd1899e6183201e311229775052002aa3b2ce
CRs-Fixed: 585483
Merge "common:Add pronto_wlan for user variant builds"
Merge ff99d34a07462ec8b6c91704ad3ecdbe6ff4416d on remote branch

Change-Id: I2e33db3d2a41a3bfd277f645000196b3fbd510eb
Merge "Merge ff99d34a07462ec8b6c91704ad3ecdbe6ff4416d on remote branch"