RK3588 Overlay: Allow DMC to use LPDDR5-6400

[HeyMeco]

Description

This is related to: https://github.com/hbiyik/rkddr which is a tool that allows to easily modify the DDR TPL for Rockchip SoC's.

Using this overlay with rkddr tool from @hbiyik we can make use of LPDDR5-6400 speeds instead of the LPDDR5-5500 set by Rockchip.

Testing

Radxa Boards:

• 5T (tested with H58G56AK6B-X069, LPDDR5-6400 module)
• 5B+ (tested with H58GG8AK8Q-X103, LPDDR5X-8533 module limited by RK3588 controller)

Testing method

• Set DMC governor to performance and confirm checking cur_freq

Results

• For GPU related tasks we see an up to 20% uplift when using glmark2-wayland with panthor driver on the terrain scene

Caution

RK3588 is validated for up to LPDDR5-5500 any damage caused to your hardware by choosing to enable this overlay as well as setting rkddr speeds is your own fault.

[HeyMeco]

Changed to draft as @hbiyik plans to do OPP table overhaul PR to be more aligned with the actual clock speeds.
Edit: Result is to keep as is.