Currently all what's needed for single file libcacard/vcard_emul_nss.c
(libnss cflags) and hw/usb/ccid-card-emulated.c (libcacard includes)
together with the libs is added to global QEMU_CFLAGS and libs_softmmu.

Use the cflags only where really used (for two mentioned files), and
libs only where needed.

While at it, rename variables to better reflect reality: libcacard_*
is really nss_*.

This needs a bit more tweaking: $(NSS_LIBS) should not contain $glib_libs
(ditto for _cflags).  But in order to fix it, some more preparations
should be made first.  So add a FIXME comment.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>