media: atmel: atmel-isc: add register description for additional modules

Add register description for additional pipeline modules: the
Defective Pixel Correction (DPC) and the Vertical and Horizontal Scaler(VHXS)

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>