fix(doc): match boot-order size to implementation

Docs had boot-order field as being u32 but code uses uint16_t.
FF-A specification does not specify a required size.

Signed-off-by: Kathleen Capella <kathleen.capella@arm.com>
Change-Id: Ia4c3fc66b9e733ea1417d34c2601bce1f81c4d32
diff --git a/docs/components/ffa-manifest-binding.rst b/docs/components/ffa-manifest-binding.rst
index 1061ca0..ee322ac 100644
--- a/docs/components/ffa-manifest-binding.rst
+++ b/docs/components/ffa-manifest-binding.rst
@@ -91,7 +91,7 @@
       - 0x2: 64k
 
 - boot-order
-   - value type: <u32>
+   - value type: <u16>
    - A unique number amongst all partitions that specifies if this partition
      must be booted before others. The partition with the smaller number will be
      booted first.