mfd: intel_soc_pmic_bxtwc: Fix TMU interrupt index

TMU interrupts are registered as a separate interrupt chip, and
hence it should start its interrupt index(BXTWC_TMU_IRQ) number
from 0. But currently, BXTWC_TMU_IRQ is defined as part of enum
bxtwc_irqs_level2 and its index value is 11. Since this index
value is used when calculating .num_irqs of regmap_irq_chip_tmu,
it incorrectly reports number of IRQs as 12 instead of actual
value of 1.

This patch fixes this issue by creating new enum of tmu IRQs and
resetting its starting index to 0.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>