Bring back rockchip-mpp support (upstream repo is now public again)

rockchip-mpp was disabled[1] a while ago because the upstream
repository was temporarily set to private[2] (hidden from the
public). Now the rockchip-mpp repositry is public[3] again and
we can re-enable this feature.

References
----------
[1] https://aur.archlinux.org/cgit/aur.git/commit/?h=ffmpeg-full&id=a224acc3d9b2d35eee6100a60e3df5822d1845dd
[2] https://github.com/HermanChen/mpp/issues/15#issuecomment-690804709
[3] https://github.com/rockchip-linux/mpp/

.SRCINFO

@@ -1,7 +1,7 @@
 pkgbase = ffmpeg-full
 	pkgdesc = Complete solution to record, convert and stream audio and video (all possible features including libfdk-aac)
 	pkgver = 4.3.1
-	pkgrel = 9
+	pkgrel = 10
 	url = https://www.ffmpeg.org/
 	arch = x86_64
 	license = custom: nonfree and unredistributable
@@ -115,6 +115,7 @@ pkgbase = ffmpeg-full
 	depends = xavs
 	depends = xavs2
 	depends = pocketsphinx
+	depends = rockchip-mpp
 	provides = libavcodec.so
 	provides = libavdevice.so
 	provides = libavfilter.so

PKGBUILD

@@ -7,7 +7,7 @@ _svt_vp9_ver='0.3.0'
 
 pkgname=ffmpeg-full
 pkgver=4.3.1
-pkgrel=9
+pkgrel=10
 pkgdesc='Complete solution to record, convert and stream audio and video (all possible features including libfdk-aac)'
 arch=('x86_64')
 url='https://www.ffmpeg.org/'
@@ -30,6 +30,7 @@ depends=(
     # AUR:
         'chromaprint-fftw' 'davs2' 'flite1-patched' 'libklvanc-git' 'openh264'
         'libopenmpt-svn' 'shine' 'vo-amrwbenc' 'xavs' 'xavs2' 'pocketsphinx'
+        'rockchip-mpp'
 )
 makedepends=(
     # official repositories:
@@ -210,7 +211,7 @@ build() {
         --enable-nvdec \
         --enable-nvenc \
         --enable-omx \
-        --disable-rkmpp \
+        --enable-rkmpp \
         --enable-v4l2-m2m \
         --enable-vaapi \
         --enable-vdpau