tools: mxsboot: calculate ECC block level dynamically

For pages of 2048 bytes the current setting of the ECC Error Correction Level
is only true for an oob size of 64 bytes and wrong for all others.

Instead of hard-coding every possible combination of page size and oob size use
the dynamic calculation of the ECC strength introduced in commit
6121560d.

Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>