thunderbolt: Refactor DROM reading

The NVM reading code has a series of gotos that potentially introduce
unexpected behaviors with retries if something unexpected has failed
to parse.

Refactor the code to remove the gotos and drop the retry logic.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
[mw: renamed root switch to host router, split device handling too]
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>