arm: sunxi: increase SYS_MALLOC_F_LEN

The current default of 0x400 for SYS_MALLOC_F_LEN is too small if any
additional drivers marked as DM_FLAG_PRE_RELOC are loaded before
relocation.

CONFIG_RSA=y which is needed for UEFI secure boot or for FIT image
verification loads the driver mod_exp_sw which has DM_FLAG_PRE_RELOC.

CONFIG_LOG=Y is another setting requiring additional early malloc
area, cf. log_init().

When running pine64-lts_defconfig with CONFIG_RSA=y and debug UART enabled
we see as output in main U-Boot

    alloc_simple() alloc space exhausted

With this patch the default values of SYS_MALLOC_F_LEN and
SPL_SYS_MALLOC_F_LEN on ARCH_SUNXI are raised to 0x2000.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>