Platform:corstone1000: BL2 uses GPT layout

Adabt BL2 to use GPT parser find tfm and fip partitions, and then
extract info to populate MCUBOOT flashmap.

Side changes required:
Borrow 2k of BL2 code memory to Data memory (during linking)
i.e. Increase BL2_DATA_GAP_SIZE and decrease SE_BL2_PARTITION_SIZE

Signed-off-by: Mohamed Omar Asaker <mohamed.omarasaker@arm.com>
Change-Id: I62bdabaf13510d4a63d95643831ec5f48c9ca906