media: platform: sti: remove bdisp_dbg_declare() and hva_dbg_declare()

We already have the DEFINE_SHOW_ATTRIBUTE. There is no need to define
bdisp_dbg_declare and hva_dbg_declare, so remove them. Also use
DEFINE_SHOW_ATTRIBUTE to simplify some code.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Reviewed-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>