nios2: remove unused statistic counters

Removed some statistic counters to improve the performance of the handler.

Signed-off-by: Bernd Weiberg <bernd.weiberg@siemens.com>
Signed-off-by: Ley Foon Tan <lftan@altera.com>

nios2: fixed variable imm16 to s16

Fxid variable imm16 to s16 instead of u16, offset might be negative.

Signed-off-by: Bernd Weiberg <bernd.weiberg@siemens.com>
Signed-off-by: Ley Foon Tan <lftan@altera.com>

nios2: Exception handling

This patch contains the exception entry code (kernel/entry.S) and
misaligned exception.

Signed-off-by: Ley Foon Tan <lftan@altera.com>