[U-Boot] Add support for imxrt

[Giulio Benetti]

Hi Fabio and Stefano,

On 9/29/19 9:40 PM, Fabio Estevam wrote:
> We try to use DM in U-Boot proper as much as possible, but using DM in
> SPL is currently not a requirement, especially due to internal RAM
> size constraints.
IOMUXC and LPUART(using 24Mhz clock) work correctly using DM.

About clk drivers, I've seen all around that they are very shrinked 
Linux's version drivers. Would it make sense to add complete clk driver 
in u-boot starting from Linux one(i.e. vf610) or it would only grow 
size? I mean, after adding initial support I would like to add Lcd 
controller driver etc. etc. so a complete driver would be useful.
Instead what I see on IMX6 clk driver is only a subsection of all PLLs 
and ref_sel to start Linux up.

I wait for your answer before proceeding with clk.

In the meanwhile I clean up and rebase then I begin adding sdram driver 
for semc.

If you want you can take a look here:
https://github.com/giuliobenetti/u-boot/commits/imxrt-dts

btw I need to clean up everything and rebase, so at the moment it's a mess.
It's based on U-boot 2019.10

Best regards
-- 
Giulio Benetti
Benetti Engineering sas