ipmi_si: Introduce ipmi_panic_event_str[] array

Instead of repeating twice the constant literals, introduce
ipmi_panic_event_str[] array. It allows to simplify the code
with help of match_string() API.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Message-Id: <20210402174334.13466-6-andriy.shevchenko@linux.intel.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>