Revert "arch/riscv: Use arch_switch() for context swap"

This reverts commit be28de692c5e2c5546841c49d6a85d5f046474a4.

The purpose of this commit will be reintroduced later on top of
a cleaner codebase.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
7 files changed