build: restrict usage of CTX_INCLUDE_EL2_REGS

CTX_INCLUDE_EL2_REGS is used to save/restore EL2 registers and
it should be only used when there is SPMD or RME enabled.

Make CTX_INCLUDE_EL2_REGS an internal macro and remove
from documentation.

Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
Change-Id: I6a70edfd88163423ff0482de094601cf794246d6
diff --git a/docs/getting_started/build-internals.rst b/docs/getting_started/build-internals.rst
new file mode 100644
index 0000000..a015d71
--- /dev/null
+++ b/docs/getting_started/build-internals.rst
@@ -0,0 +1,14 @@
+Internal Build Options
+======================
+
+|TF-A| internally uses certain options that are not exposed directly through
+:ref:`build-options <build options>` but enabled or disabled indirectly and
+depends on certain options to be enabled or disabled.
+
+.. _build_options_internal:
+
+-  ``CTX_INCLUDE_EL2_REGS``: This boolean option provides context save/restore
+   operations when entering/exiting an EL2 execution context. This is of primary
+   interest when Armv8.4-SecEL2 or RME extension is implemented.
+   Default is 0 (disabled). This option will be set to 1 (enabled) when ``SPD=spmd``
+   and ``SPMD_SPM_AT_SEL2`` is set or when ``ENABLE_RME`` is set to 1 (enabled).
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 402de13..7cd9b2b 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -164,12 +164,6 @@
    is on hardware that does not implement AArch32, or at least not at EL1 and
    higher ELs). Default value is 1.
 
--  ``CTX_INCLUDE_EL2_REGS`` : This boolean option provides context save/restore
-   operations when entering/exiting an EL2 execution context. This is of primary
-   interest when Armv8.4-SecEL2 extension is implemented. Default is 0 (disabled).
-   This option must be equal to 1 (enabled) when ``SPD=spmd`` and
-   ``SPMD_SPM_AT_SEL2`` is set.
-
 -  ``CTX_INCLUDE_FPREGS``: Boolean option that, when set to 1, will cause the FP
    registers to be included when saving and restoring the CPU context. Default
    is 0.
diff --git a/docs/getting_started/index.rst b/docs/getting_started/index.rst
index 3fbf48d..5ebabea 100644
--- a/docs/getting_started/index.rst
+++ b/docs/getting_started/index.rst
@@ -10,6 +10,7 @@
    initial-build
    tools-build
    build-options
+   build-internals
    image-terminology
    porting-guide
    psci-lib-integration-guide