x86: conga-qeval20-qa3-e3845: Select SERIAL_RX_BUFFER via Kconfig

To support more input characters (longer stings pasted into the U-Boot
prompt) without dropping, lets selects the recently added UART RX
buffer for these boards.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/congatec/conga-qeval20-qa3-e3845/Kconfig b/board/congatec/conga-qeval20-qa3-e3845/Kconfig
index e1fae73..9e44413 100644
--- a/board/congatec/conga-qeval20-qa3-e3845/Kconfig
+++ b/board/congatec/conga-qeval20-qa3-e3845/Kconfig
@@ -25,6 +25,7 @@
 	select SPI_FLASH_STMICRO
 	imply SPI_FLASH_SPANSION
 	imply SPI_FLASH_WINBOND
+	select SERIAL_RX_BUFFER
 
 config PCIE_ECAM_BASE
 	default 0xe0000000