i2c: lpi2c: implement xfer_atomic callback

Rework the read and write code paths in the driver to support operation
in atomic contexts. To achieve this, the driver must not rely on IRQs
or perform any scheduling, e.g., via a sleep or schedule routine.

Implement atomic, sleep-free, and IRQ-less operation. This increases
complexity but is necessary for atomic I2C transfers required by some
hardware configurations, e.g., to trigger reboots on an external PMIC chip.

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Carlos Song <carlos.song@nxp.com>
Tested-by: Primoz Fiser <primoz.fiser@norik.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250718133429.67219-3-francesco@dolcini.it