nitro_enclaves: Use internal cross-reference for kernel docs links

Convert links to kernel docs pages from external link to internal
cross-references.

Signed-off-by: Bagas Sanjaya <[email protected]>

Author: bagasme

Documentation/virt/ne_overview.rst

@@ -91,10 +91,10 @@ running in the primary VM via a poll notification mechanism. Then the user space
 enclave process can exit.
 
 [1] https://aws.amazon.com/ec2/nitro/nitro-enclaves/
-[2] https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html
+[2] Documentation/admin-guide/mm/hugetlbpage.rst
 [3] https://lwn.net/Articles/807108/
-[4] https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
+[4] Documentation/admin-guide/kernel-parameters.rst
 [5] https://man7.org/linux/man-pages/man7/vsock.7.html
-[6] https://www.kernel.org/doc/html/latest/x86/boot.html
-[7] https://www.kernel.org/doc/html/latest/arm64/hugetlbpage.html
-[8] https://www.kernel.org/doc/html/latest/arm64/booting.html
+[6] Documentation/arch/x86/boot.rst
+[7] Documentation/arch/arm64/hugetlbpage.rst
+[8] Documentation/arch/arm64/booting.rst