[config][arm64] Add PL031 RTC driver to config.

The Zircon VMM emulates a PL031 clock. Add support to Linux to allow
us to get the host's wall time.

Change-Id: I2544556b19cdeaead87b97434682834d9e934ded

arch/arm64/configs/machina_defconfig

diff --git a/arch/arm64/configs/machina_defconfig b/arch/arm64/configs/machina_defconfig
index b088b90..ffccd3a 100644
--- a/arch/arm64/configs/machina_defconfig
+++ b/arch/arm64/configs/machina_defconfig
@@ -28,3 +28,10 @@
 CONFIG_EXT4_FS=y
 CONFIG_ROMFS_FS=y
 CONFIG_TMPFS=y
+
+# Support for PL031 RTC, emulated by the VMM.
+CONFIG_RTC_LIB=y
+CONFIG_RTC_CLASS=y
+CONFIG_RTC_HCTOSYS=y
+CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
+CONFIG_RTC_DRV_PL031=y