mtd: rawnand: denali_dt: add reset controlling

According to the Denali NAND Flash Memory Controller User's Guide,
this IP has two reset signals.

  rst_n:     reset most of FFs in the controller core
  reg_rst_n: reset all FFs in the register interface, and in the
             initialization sequencer

This commit supports controlling those reset signals.

It is possible to control them separately from the IP point of view
although they might be often tied up together in actual SoC integration.

The IP spec says, asserting only the reg_rst_n without asserting rst_n
will cause unpredictable behavior in the controller. So, the driver
deasserts ->rst_reg and ->rst in this order.

Another thing that should be kept in mind is the automated initialization
sequence (a.k.a. 'bootstrap' process) is kicked off when reg_rst_n is
deasserted.

When the reset is deasserted, the controller issues a RESET command
to the chip select 0, and attempts to read out the chip ID, and further
more, ONFI parameters if it is an ONFI-compliant device. Then, the
controller sets up the relevant registers based on the detected
device parameters.

This process might be useful for tiny boot firmware, but is redundant
for Linux Kernel because nand_scan_ident() probes devices and sets up
parameters accordingly. Rather, this hardware feature is annoying
because it ends up with misdetection due to bugs.

So, commit 0615e7ad ("mtd: nand: denali: remove Toshiba and Hynix
specific fixup code") changed the driver to not rely on it.

However, there is no way to prevent it from running. The IP provides
the 'bootstrap_inhibit_init' port to suppress this sequence, but it is
usually out of software control, and dependent on SoC implementation.
As for the Socionext UniPhier platform, LD4 always enables it. For the
later SoCs, the bootstrap sequence runs depending on the boot mode.

I added usleep_range() to make the driver wait until the sequence
finishes. Otherwise, the driver would fail to detect the chip due
to the race between the driver and hardware-controlled sequence.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>