feat(docs): allow verbose build

If V=1 is set (or directly Q="") in the 'make doc' command line, the
sphinx command that builds the documentation is displayed.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I4961c124cc52d0183371f1d4bbc0e440f5ae6e63
1 file changed