ANDROID: sched/rt: Only enable RT sync for SMP targets

The rt sync wakeup support has a condition which relies on a field that
exists only when CONFIG_SMP is defined, causing a compilation issue.
Since sync wakeup has no real meaning on a non-SMP system, we can just
drop the CONFIG_RT_GROUP_SCHED part of the #ifdef.

Fixes: da5f3cd3 ("ANDROID: sched/rt: Add support for rt sync wakeups")
Signed-off-by: J. Avila <elavila@google.com>
Change-Id: I9b95304408d323b0c1017bd33746ecfbb2b35808