rootfs-handoff: Milestone E - add boot policy parameters

rootfs-handoff: Milestone E - add boot policy parameters

- Add rootfstype= parameter to specify explicit filesystem type
- Add rootflags= parameter for comma-separated mount options (ro, nosuid, nodev, noexec)
- Add ro/rw flags to control read-only or read-write mount
- Add rootdelay=N parameter to wait N seconds before mounting
- Add rootwait flag (recognized but not yet implemented)
- Parse and apply mount flags to root filesystem
- Add process.h include for process_sleep()

Test Results:
- Smoke test: 131/131 PASS
- Battery test: 157/157 PASS
- Analyzer: PASS
- Zero regressions