docs(boot info): structures of the boot protocol

Add doc comment to boot info header and descriptor structures.

Change-Id: I7e8d8b8c2d8299b1c9f2160025739f6708f5236e
Signed-off-by: J-Alves <joao.alves@arm.com>
diff --git a/inc/vmapi/hf/ffa.h b/inc/vmapi/hf/ffa.h
index dde35bb..6109bb4 100644
--- a/inc/vmapi/hf/ffa.h
+++ b/inc/vmapi/hf/ffa.h
@@ -461,6 +461,10 @@
 /** Length in bytes of the name in boot information descriptor. */
 #define FFA_BOOT_INFO_NAME_LEN 16
 
+/**
+ * The FF-A boot info descriptor, as defined in table 5.8 of section 5.4.1, of
+ * the FF-A v1.1 EAC0 specification.
+ */
 struct ffa_boot_info_desc {
 	char name[FFA_BOOT_INFO_NAME_LEN];
 	uint8_t type;
@@ -526,6 +530,10 @@
 /** Length in bytes of the signature in the boot descriptor. */
 #define FFA_BOOT_INFO_HEADER_SIGNATURE_LEN 4
 
+/**
+ * The FF-A boot information header, as defined in table 5.9 of section 5.4.2,
+ * of the FF-A v1.1 EAC0 specification.
+ */
 struct ffa_boot_info_header {
 	uint32_t signature;
 	uint32_t version;