Factor-out ISP specific functions to method-based call tables.

In anticipation of ISP24xx/ISP25xx support, factor-out ISP
specific functions into a method-based call table.
Signed-off-by: NAndrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>