Missing for enabling HW media decoder in naopc-t6 board

Missing for enabling HW media decoder in naopc-t6 board

In nanopc-t6 board environment, bsp bbappend add
gstreamer1.0-rockchip-rockchipmpp to RDEPEND of
gstreamer1.0-rockchip.  But it's masked by BBMASK.

This patch change BBMASK to enable that bbappend.

Bug-AGL: SPEC-5327

Change-Id: Iadbf4db16b2d247389141550f9ab0dc64be8b333
Signed-off-by: Naoto Yamaguchi <naoto.yamaguchi@aisin.co.jp>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/30700
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>