Merge changes from topic "ddr_map" into integration

* changes:
  stm32mp1: use stm32mp_get_ddr_ns_size() function
  stm32mp1: set XN attribute for some areas in BL2
  stm32mp1: dynamically map DDR later and non-cacheable during its test
  stm32mp1: add a function to get non-secure DDR size