Mirror configs for Rockchip BSP packages.

How to use:
1/ Put mirror.conf under build/conf
2/ Include it when running bitbake, e.g.:
build# bitbake core-image-minimal -r conf/mirror.conf

NOTE:
The older meta-rockchip(e.g. release-1.2.0) puts rockchip-alsa-config
in the alsa-lib package, which needs to uncomment these:
## For older meta-rockchip.
#SRC_URI_pn-alsa-lib = " \
#        ftp://ftp.alsa-project.org/pub/lib/${BP}.tar.bz2 \
#        ${RK_MIRROR};branch=alsa-config;name=rk-alsa-config \
#"
#SRC_URI_pn-alsa-lib-native = "${SRC_URI_pn-alsa-lib}"
#SRC_URI_pn-nativesdk-alsa-lib = "${SRC_URI_pn-alsa-lib}"