[media] media: Sanitise the reserved fields of the G_TOPOLOGY IOCTL arguments

The argument structs are used in arrays for G_TOPOLOGY IOCTL. The
arguments themselves do not need to be aligned to a power of two, but
aligning them up to the largest basic type alignment (u64) on common ABIs
is a good thing to do.

The patch changes the size of the reserved fields to 5 or 6 u32's and
aligns the size of the struct to 8 bytes so we do no longer depend on the
compiler to perform the alignment.

While at it, add __attribute__ ((packed)) to these structs as well.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>