uDisplay fast drawing on RGB displays

[s-hadinger]

Description:

@gemu2015 I optimized uDisplay's pushColors() for RGB displays. The main problem was that Cache_WriteBack_Addr() was called from the inner loop. Actually you only need to write-back cache once the copy is done via esp_cache_msync().

I also isolated RGB display to have more compact code.

The code is inspired from inner loops in https://github.com/espressif/esp-idf/blob/master/components/esp_lcd/rgb/esp_lcd_panel_rgb.c

I will try to adapt the code for DisplayRotate > 0 with optimized loops as well.

Before:
LVG: Refreshed 28800 pixels in 38 ms (757 pix/ms)

Now:
LVG: Refreshed 57600 pixels in 5 ms (11520 pix/ms) which means that upgrading the full 480x480 screen takes 20ms

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.6
• The code change is tested and works with Tasmota core ESP32 V.3.0.0
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass