Set CONFIG_SYS_PROMPT

- Set CONFIG_SYS_PROMPT to "uboot=>", to align with the prompt on Enterprise.
Should help simplify a few codepaths in testing.

Change-Id: I5b02f3542cf9013d81e4ca09db093eadac86f4d3
diff --git a/configs/mt8516_coral_defconfig b/configs/mt8516_coral_defconfig
index c1ef61b..b40b058 100644
--- a/configs/mt8516_coral_defconfig
+++ b/configs/mt8516_coral_defconfig
@@ -89,3 +89,4 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_CMD_USB_MASS_STORAGE=y
 CONFIG_SUPPORT_EMMC_BOOT=y
+CONFIG_SYS_PROMPT="u-boot=> "