boot/bootutil/ram_load: Add flash area pointer to bootloader state

Since 1b2fc096, many places now reuse
the flash area pointer from the bootloader state. Unfortunately, some
RAM load usage (on single loader or runtime-source sample) didn't set up
the flash area pointer on the bootloader state, so they were broken.

This patch fixes that by adding the flash area pointer to the created
bootloader states - directly or via a new parameter to
boot_load_image_from_flash_to_sram().

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>