libmodprobe: allow module with soft dependencies to load in parallel

1. integrate modules which have soft dependencies into parallel loading flow. First, check the soft dependencies are in `module.load`  list. If yes, regard soft dependencies as hard dependencies and load the modules only when their dependencies are loaded. If not, abandon these soft dependencies.

2. also add an allowlist and use the term "load_sequential=1" to load specific modules in sequential.

Test: R4 saves 350ms+ (48%) to load all modules
Bug: 229794277
Signed-off-by: chungkai <chungkai@google.com>
Change-Id: I904fe31cd02f9d499dadc537335cadc88d8add70