gpiolib: don't build HTE code with CONFIG_HTE disabled

Hardware timestamping is only used on tegra186 platforms but we include
the code and export the symbols everywhere. Shrink the binary a bit by
compiling the relevant functions conditionally.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250217103922.151047-2-brgl@bgdev.pl


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>