Added regshift parameter after base address in i8254_load(), i8254_mm_load(),

Added regshift parameter after base address in i8254_load(), i8254_mm_load(),
i8254_read(), i8254_mm_read(), i8254_write(), i8254_mm_write(),
i8254_set_mode(), i8254_mm_set_mode(), i8254_status(), i8254_mm_status().
The offsets to the four 8253/8254 registers will be shifted left by this
amount.  This is to cater for cards where the four registers do not occupy
consecutive bytes.