configs: pumpkin: increase fastboot buf size

The current fastboot buf size is a little bit small which means that
when we flash files, the files will be split in a lot of blocks.
Increase the buf size in order to reduce the overhead of many small
block.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
diff --git a/configs/pumpkin_defconfig b/configs/pumpkin_defconfig
index 5c5acf2..4adf478 100644
--- a/configs/pumpkin_defconfig
+++ b/configs/pumpkin_defconfig
@@ -49,7 +49,7 @@
 CONFIG_CLK=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x4d000000
-CONFIG_FASTBOOT_BUF_SIZE=0x700000
+CONFIG_FASTBOOT_BUF_SIZE=0x4000000
 CONFIG_FASTBOOT_FLASH=y
 CONFIG_FASTBOOT_FLASH_MMC_DEV=0
 CONFIG_DM_GPIO=y