lib: el3_runtime: Conditionally save/restore EL2 NEVE registers

Include EL2 registers related to Nested Virtualization in EL2 context
save/restore routines if architecture supports it and platform wants to
use these features in Secure world.

Change-Id: If006ab83bbc2576488686f5ffdff88b91adced5c
Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 40fc5db..8adf4ad 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -161,6 +161,10 @@
    registers to be included when saving and restoring the CPU context. Default
    is 0.
 
+-  ``CTX_INCLUDE_NEVE_REGS``: Boolean option that, when set to 1, will cause the
+   Armv8.4-NV registers to be saved/restored when entering/exiting an EL2
+   execution context. Default value is 0.
+
 -  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, enables
    Pointer Authentication for Secure world. This will cause the ARMv8.3-PAuth
    registers to be included when saving and restoring the CPU context as