Allow using feature to enable boot-time-monitor This commit allows controlling boot-time-monitor enablement by setting DISTRO_FEATURES. This is part of the effort of making boot-time-monitor as TTF distro default. Tested: Manually verified building receipt and image. Both are controlled by this flag. Fusion-Link: - Platform11: - http://fusion2/5a5d7cfd-f5f8-3c3e-b2d9-c17b53ba782b - http://fusion2/aeaa8fe6-e315-3c5b-aa9d-689c848c16a8 - Platform5: http://fusion2/477da009-63d0-4c1c-983e-6412e47bd936 - Platform15: http://fusion2/b1836475-4a9e-328d-ba36-a81d99d60602 - Platform17: http://fusion2/71351e10-7521-3bb7-a7cb-7c91abc670a8 Google-Bug-Id: 386135750 Change-Id: I03f56cd2574442a8a3e095094586f0a52976aed1 Signed-off-by: Medicine Yeh <medicineyeh@google.com>