feat(stm32mp1): add define for external scratch buffer for nand devices

Override the default platform function to use an external buffer
on STM32MP13 platform.
It allows to use a temporary buffer located at the SRAM1 memory end.

Signed-off-by: Lionel Debieve <lionel.debieve@foss.st.com>
Change-Id: Ibd84bb336c60af24608268916b3a18bb5a0fa3db
2 files changed