arm: layerscape: Add sfp driver

arm: layerscape: Add sfp driver

This adds a driver for the Security Fuse Processor (SFP) present on
LS1012A, LS1021A, LS1043A, and LS1046A processors. It holds the
Super-Root Key (SRK), One-Time-Programmable Master Key (OTPMK), and
other "security" related fuses. Similar devices (sharing the same name)
are present on other processors, but for the moment this just supports
the LS2 variants.

The mirror registers are loaded during power-on reset. All mirror
registers must be programmed or read at once. Because of this, `fuse
prog` will program all fuses, even though only one might be specified.
To prevent accidentally burning through all your fuse programming cycles
with something like `fuse prog 0 0 A B C D`, we limit ourselves to one
programming cycle per reset. Fuses are numbered based on their address.
The fuse at 0x1e80200 is 0, the fuse at 0x1e80204 is 1, etc.

The TA_PROG_SFP supply must be enabled when programming fuses, but must
be disabled when reading them. Typically this supply is enabled by
inserting a jumper or by setting a register in the board's FPGA. I've
also added support for using a regulator. This could be helpful for
automatically issuing the FPGA write, or for toggling a GPIO controlling
the supply.

I suggest using the following procedure for programming:

1. Override the fuses you wish to program
   => fuse override 0 2 A B C D
2. Inspect the values and ensure that they are what you expect
   => fuse sense 0 2 4
3. Enable TA_PROG_SFP
4. Issue a program command using OSPR0 as a dummy. Since it contains the
   write-protect bit you will usually want to write it last anyway.
   => fuse prog 0 0 0
5. Disable TA_PROG_SFP
6. Read back the fuses and ensure they are correct
   => fuse read 0 2 4

Signed-off-by: Sean Anderson <sean.anderson@seco.com>