This patch fixes the delay loop used to wake up the BPMP during SC7 exit.
The earlier loop would fail just when the timer was about to wrap-around
(e.g. when TEGRA_TMRUS_BASE is 0xfffffffe, the target value becomes 0,
which would cause the loop to exit before it's expiry).

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>