Implement listen mode for UART in KE02Z

[forGGe]

Continuation of #229 KE02 platform UART must be extended with listen mode, similar to stm32 (#226)

Example must be created (most likely based on HM-10) to illustrate usage of the listen mode.

Roadmap:

• [ ] IRQ module
• [ ] Implementation
• [ ] Platform docs
• [ ] HM-10 (or similar) example for KE02 UART

Depends on #230