x86: Do not use IRQ priority for DPL

Fixes a bug in the x86 IRQ_CONNECT_STATIC() macro that resulted in setting
the DPL for the interrupt to the IRQ priority level.

Note 1: Using a proper value for the DPL (instead of the priority) prevents
the corruption of the other IDT fields.

Note 2: The priority of the IRQ is completely ignored.

Change-Id: Ic9f59bd91db4b356263f533cc26a0168b1d236e1
Signed-off-by: Peter Mitsis <peter.mitsis@windriver.com>