drm/i915: don't specify the IRQ register in the gen2 macros

Like the gen3+ macros, the gen2 versions of the IRQ initialization
macros take the register name in the 'type' argument. But gen2 only
has one set of registers, so there's really no need to specify the
type. This commit removes the type argument and uses the registers
directly instead of passing them through variables.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190410235344.31199-3-paulo.r.zanoni@intel.com