ST7789: Add mirrored display modes to support 2" rounded rectangle TFT LCD display 240*296 pixels

[FedericoBusero]

This pull request adds support for a new 2" TFT LCD display with a rounded rectangle form factor (240*296 pixels) and ST7789 command set.

The display can be used using following settings:

#define ST7789_DRIVER
#define TFT_HEIGHT 296
#define CGRAM_OFFSET
#define TFT_RGB_ORDER TFT_BGR
#define TFT_INVERSION_OFF
#define SPI_FREQUENCY  80000000

However, the image is mirrored and in some rotations, there is a 24-pixel offset. This pull request addresses these issues by adding support for four additional rotations (4-7) to the ST7789 driver to enable mirroring. In case CGRAM_OFFSET is defined and the height equals 296 pixels, the offset is set when the display is in a mirrored rotation mode.

An alternative implementation for the mirror issue could be the introduction of a define ST7789_MIRROR similar to M5STACK. Please indicate which solution is preferred.

[cheops]

I tested this change with a screen like this
works ok for me

[cheops]

I tested this change with a screen like this
works ok for me