imx8mp_evk: Increase CONFIG_SYS_MALLOC_F_LEN

When booting imx8mp-evk the following allocation error
message is seen:

U-Boot 2021.01-rc3-00200-ge668bec9

 (Dec 21 2020 - 14:36:42 -0300)

alloc space exhausted

Fix it by increasing CONFIG_SYS_MALLOC_F_LEN to 0x10000 like it
is done on other i.MX8MM/8MN boards.
Reported-by: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>

configs/imx8mp_evk_defconfig

@@ -4,7 +4,7 @@ CONFIG_SYS_TEXT_BASE=0x40200000
 CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
-CONFIG_SYS_MALLOC_F_LEN=0x8000
+CONFIG_SYS_MALLOC_F_LEN=0x10000
 CONFIG_ENV_SIZE=0x1000
 CONFIG_ENV_OFFSET=0x400000
 CONFIG_SYS_I2C_MXC_I2C1=y