clk: tegra: Add PLLE HW power sequencer control

PLLE has a hardware power sequencer logic which is a state machine
that can power on/off PLLE without any software intervention. The
sequencer has two inputs, one from XUSB UPHY PLL and the other from
SATA UPHY PLL. PLLE provides reference clock to XUSB and SATA UPHY
PLLs. When both of the downstream PLLs are powered-off, PLLE hardware
power sequencer will automatically power off PLLE for power saving.

XUSB and SATA UPHY PLLs also have their own hardware power sequencer
logic. XUSB UPHY PLL is shared between XUSB SuperSpeed ports and PCIE
controllers. The XUSB UPHY PLL hardware power sequencer has inputs
from XUSB and PCIE. When all of the XUSB SuperSpeed ports and PCIE
controllers are in low power state, XUSB UPHY PLL hardware power
sequencer automatically power off PLL and flags idle to PLLE hardware
power sequencer. Similar applies to SATA UPHY PLL.

PLLE hardware power sequencer has to be enabled after both downstream
sequencers are enabled.

This commit adds two helper functions:
1. tegra210_plle_hw_sequence_start() for XUSB PADCTL driver to enable
   PLLE hardware sequencer at proper time.

2. tegra210_plle_hw_sequence_is_enabled() for XUSB PADCTL driver to
   check whether PLLE hardware sequencer has been enabled or not.

Signed-off-by: JC Kuo <jckuo@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>