Add ISP24xx definitions.

Add requisite structure definitions and #define's for ISP24xx
support.  Also drop volatile modifiers from device_reg_* register
layouts as the members are never really accessed, only their
offsets within the layout are used during reads and writes.
Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>