[LAYER] PX30 and RK platforms support compatible with Clea OS

NOTE: This MR alone does not actually guarantee support to Rockchip CPU-based devices since some further work (e.g. migration to new Linux Kernel and U-Boot) is necessary.

Supported platforms:

• PX30
• RK3399
• RK3568

Supported boards:

• SBC-3.5-PX30 (D23)
• SBC-3.5-RK3399 (C31)
• SBC-3.5-RK3568 (E09)

MAIN SW components (version):

• U-Boot (2017.09)
• Linux kernel (5.10)

Changes with respect to Clea OS 1.x (Kirkstone version)

• meta-seco-bsp compatibility: Ensures compatibility with the meta-seco-bsp layer, which is one of the two core components of the distribution. This layer provides a common and well-defined interface that all hardware-specific layers must adhere to.