BootParameters: Support silent boot.

* If it's a silent boot, call boot_action_silent_boot from lib.
* Otherwise, boot normally (e.g. with callbacks).

Bug: 78525346
Test: Master (sdk_google_iot_x86) builds and validated on oc-mr1-iot-dev,
* With no boot parameters, the boot is not silent,
* With normal parameters, the boot is not silent.
* With silent parameters, the boot is silent.
* With test bootactions lib, verify lib is loaded and non-silent boot
follows expected sequence and a silent boot calls
boot_action_silent_boot.

In all cases above, sample parameters are preserved.

Change-Id: I74bc9b5262fc4a181339da50726b415c3e4d3398