vaapipostproc: don't do any color conversion when GL_TEXTURE_UPLOAD

https://bugzilla.gnome.org/show_bug.cgi?id=748184 has resurrected
with commit 3e992d8a

Since gst_vaapi_find_preferred_caps_feature() returns a color format
from caps negotiation, different from the default one (NV12), the
postproc enables the color transformation. But when GL_TEXTURE_UPLOAD
feature is negotiated, no color transformation shall be done.

Nonetheless, with commit 3e992d8a the requested format changes
firstly, because there's no video sink yet, so ANY caps are
negotiated; but later, when there's a video sink and a caps
renegotiation, the GL_TEXTURE_UPLOAD is negotiated though the color
format conversion still ongoing. It is required to reset that
conversion.

This patch force default color format when GL_TEXTURE_UPLOAD is
selected as preferred, thus avoiding the color conversion.

Fixes: #157
11 jobs for no-color-conversion-gl-upload in 156 minutes and 33 seconds (queued for 1 minute and 15 seconds)
Status Job ID Name Coverage
  Preparation
passed #277153
gst indent

00:00:25

passed #277152
manifest

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  Build
passed #277154
build fedora x86_64

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passed #277155
build nodebug fedora x86_64

00:05:01

 
  Test
passed #277156
check fedora

00:03:45

 
  Full Builds
passed #279023
build cerbero android universal

00:10:17

passed #277159
build cerbero cross win32

00:44:07

passed #277160
build cerbero cross win64

00:45:56

passed #277157
build cerbero fedora x86_64

00:43:13

failed #277158
build cerbero android universal

01:00:01

 
  Apps
passed #277161
android universal examples

00:07:20