lib: gui: lvgl: align all Kconfig object names

Align all Kconfig option names with LVGL names. The followed rule:
LV_(.*) -> CONFIG_LVGL_(.*).

Also replaced LVGL boolean configuration entries using if/else/endif
with direct IS_ENABLED macro.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
19 files changed