Too noisy log output to serial console in VisionFive2 board.

[watatuki]

Description

At a VisionFIve2 board, the default u-boot bootargs is used from https://github.com/riscv/meta-riscv/blob/master/recipes-bsp/u-boot/u-boot-starfive/uEnv-visionfive2.txt. That setting is including "debug" keyword.
As a result, many systemd debug message output to serial console.

I recomend to remove "debug" from default bootarg setting.

Steps to reproduce the issue:

1. Build image for visionfive2.
2. Bootup using this image.

Describe the results you received:
many systemd debug message output to serial console.

Describe the results you expected:
Do not output many systemd debug message to serial console.