camelbackmountain_fsp: Select SERIRQ_CONTINUOUS_MODE

In commit 4f2754c
'fsp_broadwell_de: Add Kconfig switch for SERIRQ operation mode'
the default operation mode of SERIRQ was changed from continuous to quiet.
Set the mode to continuous for this mainboard to keep the behavior unchanged.

Change-Id: I7c3675d4ee8cff428621f4e64411738193e654b2
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/16576
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: York Yang <york.yang@intel.com>
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/intel/camelbackmountain_fsp/Kconfig

@@ -9,6 +9,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select TSC_MONOTONIC_TIMER
 	select INTEGRATED_UART if FSP_PACKAGE_DEFAULT
 	select HAVE_FSP_BIN if FSP_PACKAGE_DEFAULT
+	select SERIRQ_CONTINUOUS_MODE
 
 config MAINBOARD_DIR
 	string