gstreamer1.0: Transition to meson based builds

gstreamer1.0: Transition to meson based builds

* Moved 0001-gst-gstpluginloader.c-when-env-var-is-set-do-not-fal.patch
  from files/ to gstreamer1.0/ since it is gstreamer1.0 recipe specific.

* Removed M4 specific patches:
  - 0001-introspection.m4-prefix-pkgconfig-paths-with-PKG_CON.patch
  - gtk-doc-tweaks.patch
  - add-a-target-to-compile-tests.patch

* Added patches:
  - 0001-meson-build-gir-even-when-cross-compiling-if-introsp.patch
    Backport for enabling GIR support in meson based cross compilation
  - 0002-meson-Add-valgrind-feature.patch
    Make valgrind support configurable to be able to control it through
    a "valgrind" packageconfig
  - 0003-meson-Add-option-for-installed-tests.patch
    Add support for installable tests and for generating .test and shell
    scripts which can be used with the gnome-desktop-testing suite runner

* PTest support:
  By default, GStreamer does not allow for installing tests, and requires
  meson to run its unit tests. The 0003 patch fixes this by installing
  the binaries themselves and by generating accompanying .test and shell
  scripts. The scripts set up the required environment files and then
  call the test binaries. The .test file list the shell scripts as
  Exec= command line.

Signed-off-by: Carlos Rafael Giani <crg7475@mailbox.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>