Bluetooth: bap: Remove EATT dependency

The EATT support is optional for BAP. The specification mandates the
minimum MTU supported to be 64 bytes.

As per BAP_v1.0
"The Unicast Server shall support a minimum ATT_MTU of 64 octets for
one Unenhanced ATT bearer, or for at least one Enhanced ATT bearer
if the Unicast Server supports Enhanced ATT bearers."

The same applies for other BAP roles.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>