boards/stm32f3: nucleo-f302r8:ihm07m1_b16: enable LTO to fit flash

[anjiahao1]

Summary

• The nucleo-f302r8:ihm07m1_b16 (FOC motor control) configuration no
  longer links: the image overflows the STM32F302R8 64 KiB flash region
  by ~470 bytes.
• Enable GNU Full LTO (CONFIG_LTO_FULL=y) for this configuration so
  cross-module dead-code elimination brings the image back under the
  flash limit.

Impact

• Is new feature added? Is existing feature changed? NO.
• Impact on user? NO.
• Impact on build? YES — this config now builds with LTO; link time and
  memory usage increase, but the image fits flash (88% used vs. previous
  overflow).
• Impact on hardware? NO.
• Impact on documentation? NO.
• Impact on security? NO.
• Impact on compatibility? NO.
• Anything else? LTO_FULL is marked EXPERIMENTAL in Kconfig; chosen here
  because the config is otherwise unbuildable within 64 KiB.

Testing

I confirm that changes are verified on local setup and works as intended:

• Build Host(s): Ubuntu, arm-none-eabi-gcc 12.2.1
• Target(s): nucleo-f302r8:ihm07m1_b16 (STM32F302R8, 64 KiB flash)
• Build: ./tools/configure.sh nucleo-f302r8:ihm07m1_b16 && make

Testing logs before change (link fails — flash overflowed):

arm-none-eabi-ld: region `flash' overflowed by 472 bytes
Memory region         Used Size  Region Size  %age Used
           flash:       66008 B        64 KB    100.72%

Testing logs after change (links cleanly with LTO):

Memory region         Used Size  Region Size  %age Used
           flash:       57740 B        64 KB     88.10%
            sram:        5688 B        16 KB     34.72%

PR verification Self-Check

• This PR introduces only one functional change.
• I have updated all required description fields above.
• My PR adheres to Contributing Guidelines and Documentation (git commit title and message, coding standard, etc).
• My PR is still work in progress (not ready for review).
• My PR is ready for review and can be safely merged into a codebase.

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb