meta-agl-{bsp,distro}: update kernel configuration for dunfell

Changes:
- Rework CAN qdisc patch application, as it is not required for 5.4
  or newer kernels, this includes adding a linux-agl-4.19.inc for
  BSPs using 4.19.
- Remove linux-agl-4.9.inc and associated patches, as no BSP uses 4.9
  at this point.
- Remove PREFERRED_VERSION_linux-yocto from poky-agl.conf so the
  default 5.4 linux-yocto kernel will be picked up.

Bug-AGL: SPEC-3302

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I9c0eb431661641bd17320a00cdf1ed4e717a9754