[ili9xxx] Fix init for GC9A01A

[jesserockz]

What does this implement/fix?

This changes the init_lcd function to be virtual so that the GC9A01A can override it and not implement the ILI9XXX_DELAY instruction.

The GC9A01A has a function already that uses 0xFF (it is not known what it means, but it is important).

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

# Example config.yaml

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @clydebarrow, @nielsnl68, mind taking a look at this pull request as it has been labeled with an integration (ili9xxx) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}