After including generated sources to the repository, the `gitlab-cy.yml`
no longer needs to postpone building for aarch64. Also it is way
simplier now as it only needs to generate the project with meson,
and compile/test it with ninja.

Another thing that needs to be updated is the README file. We change all
references to CMake with the corresponding Meson commands.

Signed-off-by: Antonio Caggiano <antonio.caggiano@collabora.com>
Reviewed-by: Rohan Garg <rohan.garg@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>