meson: check all deps, when enabling wayland winsys
meson: check all deps, when enabling wayland winsys

Currently we check only one of the three dependencies for the wayland
winsys. As such if one is missing (say wayland-protocols) meson chokes
producing interesting output:

Run-time dependency wayland-protocols found: NO (tried pkgconfig and cmake)
Run-time dependency wayland-scanner found: YES 1.19.0
...
src/meson.build:91:4: ERROR: 'not-found' is not a pkgconfig dependency

Signed-off-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>

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