drm/etnaviv: don't fail to build on arches without PHYS_OFFSET

Some architecture ports like ARC don't provide the PHYS_OFFSET symbol.
Define it to 0 in that case, which is the most conservative default in
the usage context of the etnaviv driver.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
1 file changed