board: bsh: imx8mn_bsh_smm_s2/s2pro: enlarge CONFIG_SPL_SYS_MALLOC_F_LEN

board: bsh: imx8mn_bsh_smm_s2/s2pro: enlarge CONFIG_SPL_SYS_MALLOC_F_LEN

The commit dda454e933c6 ("serial: mxc: Support bulk enabling clocks")
breaks the booting of the BSH SMM S2 board. The analysis of the issue
revealed memory allocation failures during the registration of UART4
clocks as well as other peripherals. Increasing SYS_MALLOC_F_LEN to
0x10000 fixed the issue.

Dropping this option allows it to be set to the default value of
CONFIG_SYS_MALLOC_F_LEN, which is set by default to 0x10000 on
i.MX8M platforms.

Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>