mempool: add memx_start variable as pointer to MEMX start address
platform: add mem0_start location for platform stm32f1
platform: add mem0_start & mem1_start location for platform stm32f4
platform: add mem0_start & mem1_start location for platform stm32f429
Merge pull request #104 from slpbaby/stm32p103-fixed

platform: stm32p103: add mem0 start address