x86: Simplify architecture defined exception handling in irq_llsr()

x86: Simplify architecture defined exception handling in irq_llsr()

Instead of using switch..case for architecture defined exceptions,
simply unify the handling by printing a message of exception name,
followed by registers dump then halt the CPU.

With this unification, it also fixes the wrong exception numbers
for #MF/#AC/#MC/#XM which should be 16/17/18/19 not 15/16/17/18.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>