riscv: Kconfig: Style cleanups

The majority of the Kconfig files use a single tab for basic indentation
and a single tab followed by two whitespaces for help text indentation.
Fix the lines that don't follow this convention.

While at it, add trailing comments to endif/endmenu statements for
better readability.

* 'riscv-kconfig_cleanups' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/palmer/linux:
  riscv: Kconfig.socs: Add comments
  riscv: Kconfig.erratas: Add comments
  riscv: Kconfig: Fix indentation and add comments