Ignore BSP IMAGE_FSTYPES changes

Ignore BSP IMAGE_FSTYPES changes

Add anonymous python snippet in agl-image-minimal.inc to reset
the value of IMAGE_FSTYPES to AGL_DEFAULT_IMAGE_FSTYPES plus
AGL_EXTRA_IMAGE_FSTYPES (i.e. the value defined in poky-agl.conf).
This is a very big hammer, but at present seems the best way to
avoid the build time/space costs from BSP appends adding extra
types that are not required.

Bug-AGL: SPEC-3741
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Idad57d0371ae59058b2b1acffbeae85db97aa91d
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25846