Disable block rwbs bitwise enum in default build

Disable block rwbs bitwise enum in default build

Only generate the bitwise enumerations when
CONFIG_LTTNG_EXPERIMENTAL_BITWISE_ENUM is enabled, so the default build
does not generate traces which lead to warnings when viewed with
babeltrace 1.x and babeltrace 2 with default options.

Original commit:

  commit 23634515e7271c8c8594ad87a6685232d4eff297
  Author: Geneviève Bastien <gbastien@versatic.net>
  Date:   Tue Feb 11 11:20:27 2020 -0500

    block: Make the rwbs field as a bit field enum

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Iccf0d2b1e9ed44b280707fcc2b25a26ef7b4ca1f