raspberrypi*/50_local.conf.inc: Set Mesa version

raspberrypi*/50_local.conf.inc: Set Mesa version

Use Mesa 18.1 for Raspberry Pi 3 and Mesa 19.1 for Raspberry Pi 4.
With the older version of Mesa Weston and the home screen doesn't
launch properly on Raspberry Pi 4 therefore version 19.1 has been
ported from master branch of layer openembedded-core to layer
meta-agl-bsp/meta-raspberrypi. This solution is temporary until
the next major update of AGL from Yocto Project release Thud to
a newer release.

Bug-AGL: SPEC-2656

Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>
Change-Id: I7b3d87a42c6e65014705d98bfbd8ebdabb48eadd
Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>