doc: ti: Clarify required file names for K3 platforms

Now that we are using binman in all cases on these platforms, reword
things to be clearer that for filesystem booting we need to use a
specific name for each component.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
diff --git a/doc/board/ti/am62x_sk.rst b/doc/board/ti/am62x_sk.rst
index 3a122b0..0721ee3 100644
--- a/doc/board/ti/am62x_sk.rst
+++ b/doc/board/ti/am62x_sk.rst
@@ -169,7 +169,8 @@
 
 Target Images
 --------------
-Copy the below images to an SD card and boot:
+In order to boot we need tiboot3.bin, tispl.bin and u-boot.img.  Each SoC
+variant (GP, HS-FS, HS-SE) requires a different source for these files.
 
  - GP