Kconfigs: Correct default of "0" on hex type entries

It is not a parse error to have a default value of "0" for a "hex" type
entry, instead of "0x0".  However, "0" and "0x0" are not treated the
same even by the tools themselves. Correct this by changing the default
value from "0" to "0x0" for all hex type questions that had the
incorrect default. Fix one instance (in two configs) of a default of "0"
being used on a hex question to be "0x0". Remove the cases where a
defconfig had set a value of "0x0" to be used as the default had been
"0".

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/efi-x86_app32_defconfig b/configs/efi-x86_app32_defconfig
index 50975db..1bfc01f 100644
--- a/configs/efi-x86_app32_defconfig
+++ b/configs/efi-x86_app32_defconfig
@@ -2,7 +2,7 @@
 CONFIG_NR_DRAM_BANKS=8
 CONFIG_ENV_SIZE=0x1000
 CONFIG_DEFAULT_DEVICE_TREE="efi-x86_app"
-CONFIG_DEBUG_UART_BASE=0
+CONFIG_DEBUG_UART_BASE=0x0
 CONFIG_DEBUG_UART_CLOCK=0
 CONFIG_VENDOR_EFI=y
 CONFIG_TARGET_EFI_APP32=y