target/riscv: use struct riscv_info instead of typedef riscv_info_t

target/riscv: use struct riscv_info instead of typedef riscv_info_t

Make the main RISC-V structure more compliant with OpenOCD coding style.
Other typedefs remains as is.

Change-Id: I5657ad28fea8108fd66ab27b2dfe1c868dc5805b
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/6998
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tim Newsome <tim@sifive.com>