stm32_common: fix ram length for MCUs with non-contiguous ram
stm32_common: fix ram length for MCUs with non-contiguous ram

stm32l47xxx see RM0351, Rev 6, page 75
https://www.st.com/resource/en/reference_manual/dm00083560.pdf#page=75

stm32f303xx see RM0316, Rev 8, page 53
https://www.st.com/resource/en/reference_manual/dm00043574.pdf#page=53

stm32f334xx see RM0364, Rev 3, page 47
https://www.st.com/resource/en/reference_manual/dm00093941.pdf#page=47

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