arc: emsdp: Increase max FAT cluster size

Some especially large SD-cards come from stock formatted with
larger FAT cluster size so to accommodate those we just increase
what we expect to have here in U-Boot given we have a plenty of
space on EM SDP (16 MiB).
Signed-off-by: NAlexey Brodkin <abrodkin@synopsys.com>

configs/emsdp_defconfig

@@ -27,6 +27,6 @@ CONFIG_MMC=y
 CONFIG_MMC_DW=y
 CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y
-CONFIG_FS_FAT_MAX_CLUSTSIZE=4096
+CONFIG_FS_FAT_MAX_CLUSTSIZE=32768
 CONFIG_USE_PRIVATE_LIBGCC=y
 CONFIG_PANIC_HANG=y