docs(a3k): fix information about SATA GPT booting

Armada 3720 BootROM searches for GPT partition with partition type GUID
6828311A-BA55-42A4-BCDE-A89BB5EDECAE and completely ignores GPT
partition name. It does not check for "MARVELL BOOT PARTITION".

This fact is incorrectly documented even in official Marvell Armada 3700
Functional Specification.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I35279f39de2d12148fc16f2730a9a074dc0b58eb

docs/plat/marvell/armada/build.rst

@@ -258,7 +258,7 @@ Armada37x0 specific build options for ``mrvl_flash`` and ``mrvl_uart`` targets:
 
                 Image needs to be stored at disk LBA 0 or at disk partition with
                 MBR type 0x4d (ASCII 'M' as in Marvell) or at disk partition with
-                GPT name ``MARVELL BOOT PARTITION``.
+                GPT partition type GUID ``6828311A-BA55-42A4-BCDE-A89BB5EDECAE``.
 
 - PARTNUM