msm: restart: respect download_mode boot parameter

The download_mode flag works correctly when set as a runtime parameter,
but not when set from boot. It would work during "normal" restarts, such
as during panic, but not during watchdog bites.

Change-Id: I2e3140e7f97b2bc7e38e8021097a5640fde77486
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>