lib: utils: reset: unify naming of 'sifive_test' device

Unify all the file and function names of 'sifive_test' device, to use
the same prefix. This is also a preparatory patch for upcoming sifive
reset device.

Signed-off-by: Green Wan <green.wan@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>