misc: tegra-baseband: enhance enum with XHCI HSIC

misc: tegra-baseband: enhance enum with XHCI HSIC

We used to postpone modem booting to later stage when XHCI is used
because XHCI driver keeps HSIC bus in IDLE too early before it can
properly handle HSIC CONNECT from modem. Now XHCI driver will only keep
bus in IDLE after client enables HSIC power through sysfs node, so we
boot modem early when driver is loaded.

This change also cleans some codes.

Bug 200039977

Change-Id: Iacb5c00a11a4b11606fdf2fcffd56de4a3951483
Signed-off-by: Mark Kuo <mkuo@nvidia.com>
Reviewed-on: http://git-master/r/599934
Reviewed-by: Neil Patel <neilp@nvidia.com>
Reviewed-by: Steve Lin <stlin@nvidia.com>