mesa: guard package arch setting
mesa: guard package arch setting

Set PACKAGE_ARCH only if we have a SOCARCH defined. If we did not set
it, we assume we need to install all gallium drivers.

Reviewed-by: Norbert Wesp <6da95d5bf7a9ae873d28e5fc932fdf5af58a5861@phytec.de>
Signed-off-by: Stefan Müller-Klieser <a3e08e35e4a42be768e7d0e76ae1ba321c2a66dd@phytec.de>

PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec