Proposal: Display interface abstraction

[C47D]

This is the current proposal of the display interface abstraction. The functions declared in lvgl_tft/display_port.h are meant to be implemented by the user. In this repo they are defined in lv_port_display_espressif.c in the lv_port directory, as this is the directory were all of the ESP-IDF will end up.

The lv_disp_drv_t *drv parameter is a pointer to the registered lv_disp_drv_t, so the user will be able to know what display should they handle, in this repo we currently only use one, so there's no use for it.

In a following commit I will use this interface in two display drivers, one using SPI and the other one using I2C, so we can see the abstraction works for both kind of interfaces.

[tore-espressif]

I hope this PR is not in a big rush. We finally got more manpower to this interface design and we'd like to test it on several displays and interfaces. I'll keep you updated, thanks!

[C47D]

@tore-espressif it is not, hopefully we are going in the right direction.