[build] make mapi a subdirectory of vnd-glapi

Currently, the GLdispatch makefile recurses into the mapi/vnd-glapi
subdirectory, which then uses files out of its parent directory.  This makes it
difficult to include the mapi directory in the dist tarball because just
including it in EXTRA_DIST makes it pick up the generated Makefile in addition
to the checked-in source files.

Instead, exchange the two directories so that mapi is a subdirectory of
vnd-glapi and the former is included wholesale with EXTRA_DIST.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Brian Nguyen <brnguyen@nvidia.com>
[build] distribute files needed to build

Everything needed to actually build the driver needs to be included in something
that makes it end up in the distribution tarball.  For headers, use
noinst_HEADERS.  For everything else, use EXTRA_DIST.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Brian Nguyen <brnguyen@nvidia.com>
[build] add $(BUILT_SOURCES) to $(CLEANFILES)

The 'distclean' target should completely cleans the build directory, so that
$(builddir) contains only directories.  This means that all built sources have
to be included in CLEANFILES, or they're left behind.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Signed-off-by: Brian Nguyen <brnguyen@nvidia.com>