modules: lvgl: Fix inverting x/y if screen is rotated

https://github.com/zephyrproject-rtos/zephyr/pull/70541

 has an
issue where if the screen has been rotated, values calculated if
invert-x or invert-y are set will be overwritten.

This breaks the adafruit_2_8_tft_touch_v2 touchscreen as the
display is rotated by 90 degrees but uses invert-x and invert-y.

This change makes the invert-x and invert-y options independent
of screen rotation.

Signed-off-by: Glenn Andrews <glenn.andrews.42@gmail.com>