board/solidrun/macchiatobin: update BSP components version in documentation

Update the listed versions to match current status since commit
b4d9b515088d ("configs/solidrun_macchiatobin: bump BSP components").

All components are now from upstream so no need to state that for each
one.

Cc: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 3f0ee529083e972be9893676fab00ac50c2816c3)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/solidrun/macchiatobin/readme.txt

@@ -13,9 +13,9 @@ How to build
 ============
 
 Default configuration provides the following BSP versions:
- - Linux v5.6.3 (mainline)
- - U-Boot v2020.01 (mainline)
- - ATF v1.5-18.12.2 (Marvell)
+ - Linux v5.10.5
+ - U-Boot v2020.10
+ - ATF v2.4
 
 To build images run the following commands: