build/pkg-config: improve static linking flags

Rather than setting -Bstatic in the linker flags when doing a static link,
and then having to explicitly set -Bdynamic again afterwards, we can update
the pkg-config file to use -l:libfoo.a syntax to explicitly refer to the
static library in question. Since this syntax is not supported by meson's
pkg-config module directly, we can post-process the .pc files instead to
adjust them.

Once done, we can simplify the examples' makefiles and the docs by removing
the explicit static flag.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Acked-by: Sunil Pai G <sunil.pai.g@intel.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>