boards: stm32mp135f_dk: add touchscreen and lvgl pointer

[eszSTM]

STM32MP135F_DK board embeds a LCD screen with touchscreen driven by I2C5. GT911 touchscreen already have driver support in Zephyr so just add necessary nodes here.

[github-actions]

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[etienne-lms]

Could you break the commit message body 2nd line to fit in 74 chars?
Also, for consistency, prefer use `boards: st: stm32mp135F_dk: in the header line.

-boards: stm32mp135f_dk: add touchscreen and lvgl pointer
+boards: st: stm32mp135f_dk: add touchscreen and lvgl pointer
 
 STM32MP135F_DK board embeds a LCD screen with touchscreen driven by I2C5.
-GT911 touchscreen already have driver support in Zephyr so just add necessary nodes here.
+GT911 touchscreen already have driver support in Zephyr so just add
+necessary nodes here.
 
 Signed-off-by: ...

[eszSTM]

Modifications done after @etienne-lms comments

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud