arch/risc-v/k210: Remove QEMU support

[no1wudi]

Summary

Remove the CONFIG_K210_WITH_QEMU option and associated conditional code paths from the K210 architecture support. The reasons for removal are:

1. Simplifies code path for real hardware - Removes QEMU workarounds that complicate the codebase
2. Incorrect QEMU target - The current QEMU support uses sifive_u machine, which is not designed for K210 emulation
3. Better alternatives exist - For RISC-V QEMU simulation, the qemu-rv (rv-virt) target is a better choice
4. Renode alternative - Renode can be used as an alternative for K210 simulation if needed

Impact

• Impact on user: YES - Users can no longer use CONFIG_K210_WITH_QEMU to run K210 code on QEMU's sifive_u machine
• Impact on build: NO - No build system changes
• Impact on hardware: NO - Real hardware (Maix Bit) functionality unchanged
• Impact on documentation: YES - Removed QEMU-related documentation from maix-bit board docs
• Impact on security: NO
• Impact on compatibility: YES - Removes CONFIG_K210_WITH_QEMU config option

Testing

Build Host: Ubuntu 22.04, x86_64, GCC
Target: k210:maix-bit:nsh

Verified that the K210 real hardware configurations still compile correctly without the QEMU conditional code.

Build output:

CC:  arch/risc-v/src/k210/k210_clockconfig.c
CC:  arch/risc-v/src/k210/k210_timerisr.c
LD:  nuttx

[lupyuen]

Sorry the CI Builds won't start until the PR below is merged. Please hang on :-)

• CI: Revert GitHub Actions for Docker, by hash #18575

[lupyuen]

@no1wudi Can you Rebase With Master Branch to trigger a rebuild? Thanks!

[no1wudi]

@no1wudi Can you Rebase With Master Branch to trigger a rebuild? Thanks!

OK