sandbox: Enable NVMe driver for build testing

This enables NVMe driver on sandbox for build testing.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index ef25a4a..36b9cba 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -106,6 +106,7 @@
 CONFIG_SPI_FLASH_SST=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_DM_ETH=y
+CONFIG_NVME=y
 CONFIG_PCI=y
 CONFIG_DM_PCI=y
 CONFIG_DM_PCI_COMPAT=y