gst-plugins-bad: add dependency on librsvg

gst-plugins-bad: add dependency on librsvg

Fixes build failure if librsvg is not previously staged:

|   CC     libgstschro_la-gstschro.lo
|   CC     libgstschro_la-gstschrodec.lo
|   CCLD   libgstdfbvideosink.la
|   CC     libgstrsvg_la-gstrsvgdec.lo
|   CCLD   libgstjack.la
|   CCLD   libgstjp2k.la
| In file included from gstrsvg.c:25:
| gstrsvgdec.h:29:26: error: librsvg/rsvg.h: No such file or directory
| gstrsvgdec.h:30:32: error: librsvg/rsvg-cairo.h: No such file or directory
| gstrsvg.c: In function 'plugin_init':
| gstrsvg.c:30: warning: implicit declaration of function 'rsvg_init'
| gstrsvg.c:30: warning: nested extern declaration of 'rsvg_init'

Signed-off-by: Denys Dmytriyenko <denys@ti.com>