build(bl2): enable SP pkg loading for S-EL1 SPMC

Currently the SP package loading mechanism is only enabled when S-EL2
SPMC is selected. Remove this limitation.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: I5bf5a32248e85a26d0345cacff7d539eed824cfc
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 115b2b2..42449db 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -55,6 +55,9 @@
 -  ``BL2_AT_EL3``: This is an optional build option that enables the use of
    BL2 at EL3 execution level.
 
+-  ``BL2_ENABLE_SP_LOAD``: Boolean option to enable loading SP packages from the
+   FIP. Automatically enabled if ``SP_LAYOUT_FILE`` is provided.
+
 -  ``BL2_IN_XIP_MEM``: In some use-cases BL2 will be stored in eXecute In Place
    (XIP) memory, like BL1. In these use-cases, it is necessary to initialize
    the RW sections in RAM, while leaving the RO sections in place. This option