arm: tegra: power: Add debugfs entry for CPU regulator limit

arm: tegra: power: Add debugfs entry for CPU regulator limit

Add a debugfs node to override VDD_CPU regulator current limit
at /d/edp_reg_override. Values written to this node will be
subtracted from the regulator's current limit; EDP table will
be recalculated accodingly.

Change-Id: I523fa73bf5a8fa806477f4884e920b5866417cf3
Signed-off-by: Daniel Solomon <daniels@nvidia.com>
Reviewed-on: http://git-master/r/118815
Reviewed-by: Simone Willett <swillett@nvidia.com>
Tested-by: Simone Willett <swillett@nvidia.com>
Rebase-Id: R91e8e4722dfc06a003c3730e9a5a4a20d29a52e5