of: Add vendor prefix for Pervasive Displays

Pervasive Displays Inc. designs, develops, and manufactures low-power
electrophoretic (e-ink) display modules and supporting electronics for
commercial and industrial display applications.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1496934875-51984-2-git-send-email-noralf@tronnes.org