[BOOT] Execution contexts and more refactoring

BOOT/ENVIRON/APP/BOOTMGR/EFI/efientry.c

@@ -37,8 +37,9 @@ Arguments:
 
 Return Value:
 
+    EFI_SUCCESS if successful.
     EFI_INVALID_PARAMETER if EfiInitCreateInputParameters() fails.
-    Any status code returned by EfiGetEfiStatusCode(BmMain()).
+    Any other error code if BmMain() fails.
 
 --*/
 
@@ -54,7 +55,7 @@ Return Value:
     }
 
     //
-    // Transfer control to the firmware-independent boot manager.
+    // Transfer control to the firmware-independent boot manager code.
     //
     return EfiGetEfiStatusCode(BmMain(InputParameters));
 }