fix(el3-spmc): add datastore linker script markers

Datastore symbol used by EL3 SPMC is not relocated at
boot time when using ENABLE_PIE=1.
Use linker script markers instead of symbol.

Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
Change-Id: If22d2fc8deacc74c73d7dc51bb70093935d9fa2b
3 files changed