sunxi-cedarx: add CedarX hardware video decoding library

[Thomas: rename package to sunxi-cedarx, improve help text
description, install libraries with executable permissions to make
sure they get stripped at the end of the build.]

Signed-off-by: Spenser Gilliland <spenser@gillilanding.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>