target/riscv: move read redirection for `priv` to `riscv-013.c`

The reason for the change is a conflict: `dcsr[5]` is `dcsr.v` in
current spec, but it is `dcsr.debugint` in 0.11. This causes `priv`
register to be read incorrectly.

Change-Id: If2d8fdcd8536afa4c7149c453101b00ce0df1ce0
Signed-off-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>