doc/advanced: use proper alignment in the example boot-mbr-switch layout
doc/advanced: use proper alignment in the example boot-mbr-switch layout

The unusual sizes distract from the main topic this section and could
confuse the reader into using unaligned partitions.

Signed-off-by: Jan Luebbe <3a82f1ac4ad59607a20f180f1c67ac8ba31ad0d5@pengutronix.de>

rauc/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc