srcu: Define SRCU_READ_FLAVOR_ALL in terms of symbols

srcu: Define SRCU_READ_FLAVOR_ALL in terms of symbols

This commit defines SRCU_READ_FLAVOR_ALL in terms of the
SRCU_READ_FLAVOR_* definitions instead of a hexadecimal constant.

Suggested-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>