docs: marvell: Update info about WTMI_IMG option

Default WTMI_IMG value was documented incorrectly. Also WTMI_IMG name may
be misleading as this option does not specify full WTMI image, just a main
loop (e.g. fuse.bin or custom RTOS image) without hardware initialization
code (DDR, CPU and clocks).

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I3de4a27ce2165b962fa628c992fd8f80151efd7c
1 file changed