bsps/stm32h7: Workaround STM32 H7 errata by enforcing aligned access only

The patch changes compiler ABI flags option and adds -mno-unaligned-access
there. Usage of this option is also officially recommended way
by the errata document how to work around the issue. For more details
about the errata please see referenced issue number.

Closes #5110.

spec/build/bsps/arm/stm32h7/abi.yml

@@ -15,12 +15,14 @@ default:
   - -mcpu=cortex-m4
   - -mfpu=fpv4-sp-d16
   - -mfloat-abi=hard
+  - -mno-unaligned-access
 - enabled-by: true
   value:
   - -mthumb
   - -mcpu=cortex-m7
   - -mfpu=fpv5-d16
   - -mfloat-abi=hard
+  - -mno-unaligned-access
 description: |
   ABI flags
 enabled-by: true