imx: kontron-sl-mx8mm: Increase CONFIG_SPL_MAX_SIZE

imx: kontron-sl-mx8mm: Increase CONFIG_SPL_MAX_SIZE

The limit of 0x27000 (156 KiB) was valid at times the DDR firmware
required a fixed amount of 96 KiB of space. Now that we use binman
to include the DDR firmware it only needs around 57 KiB of space and
there is more room for the SPL.

Increase the max SPL size to 196 KiB so there is still 60 KiB for DDR
firmware. This allows us to enable USB and SDP support in SPL.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>