asahi: Make libasahi_lib depend on libasahi_decode

asahi: Make libasahi_lib depend on libasahi_decode

The track_alloc and track_free symbols are used, we need to link them in.
Depending on build flags / environment / etc, fixes the potential build error
hit by a CI job:

mold: error: undefined symbol: agxdecode_track_alloc
>>> referenced by agx_device.c
>>>               src/asahi/lib/libasahi_lib.a(src/asahi/lib/libasahi_lib.a.p/agx_device.c.o):(agx_shmem_alloc)>>> referenced by agx_device.c
>>>               src/asahi/lib/libasahi_lib.a(src/asahi/lib/libasahi_lib.a.p/agx_device.c.o):(agx_bo_create)
mold: error: undefined symbol: agxdecode_track_free
>>> referenced by agx_device.c
>>>               src/asahi/lib/libasahi_lib.a(src/asahi/lib/libasahi_lib.a.p/agx_device.c.o):(agx_bo_unreference)

...when trying to link with libasahi_lib without libasahi_decode for unit tests.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19871>