mfd: tps65219: Implement LOCK register handling for TPS65214

mfd: tps65219: Implement LOCK register handling for TPS65214

The TPS65214 PMIC variant has a LOCK_REG register that prevents writes to
nearly all registers when locked. Unlock the registers at probe time and
leave them unlocked permanently.

This approach is justified because:
- Register locking is very uncommon in typical system operation
- No code path is expected to lock the registers during runtime
- Adding a custom regmap write function would add overhead to every
  register write, including voltage changes triggered by CPU OPP
  transitions from the cpufreq governor which could happen quite
  frequently

Cc: stable@vger.kernel.org
Fixes: 7947219ab1a2d ("mfd: tps65219: Add support for TI TPS65214 PMIC")
Reviewed-by: Andrew Davis <afd@ti.com>
Signed-off-by: Kory Maincent (TI.com) <kory.maincent@bootlin.com>
Link: https://patch.msgid.link/20251218-fix_tps65219-v5-1-8bb511417f3a@bootlin.com
Signed-off-by: Lee Jones <lee@kernel.org>