boards: mpfs_icicle: remove no compiler optimization

Using CONFIG_NO_OPTIMIZATION results in larger stack sizes, which in
turn result in stack overflows for some of the sample appplications
when built for the mpfs_icicle.
This option is better served at the application level when debugging
rather than at the default level of the board.
Remove CONFIG_NO_OPTIMIZATION=y from mpfs_icicle_defconfig.

This fixes issue reported in #55466

Signed-off-by: Conor Paxton <conor.paxton@microchip.com>