[ACPI] acpi_register_gsi() fix needed for ACPICA 20051021

Use the #define for ACPI_LEVEL_SENSITIVE instead of assuming
non-zero, because ACPICA 20051021 changes its value to zero.

Also, use uniform variable names:
edge_level -> triggering
active_high_low -> polarity

Signed-off-by: Len Brown <len.brown@intel.com>