libkrunfw: Add virtio-rtc driver support

Backport virtio-rtc driver from upstream Linux kernel
to enable RTC and PTP clock support in libkrun guests.

Added 4 upstreamed patches on virtio_rtc
Enabled virtio_rtc kernel configs
This allows libkrun guests to:
- Access host time via /dev/rtc* (RTC class driver)
- Access PTP clocks via /dev/ptp* (for time synchronization)
- Set alarms to wake from suspend
- Use cross-timestamping on ARM platforms

The driver has been tested with rust-vmm vhost-device-rtc backend.

Upstream commits:
- 0623c759276885c3ae88197ba6fb5c9c6ba8612f
- 9a17125a18f9ae1e1233a8e2d919059445b9d6fd
- e2ef16757bbe1d4566093179944e9ebe730b2701
- 9d4f22fd563e0cd02e8448e84d057e7c0132a586

Upstream patch author: Peter Hilber <quic_philber@quicinc.com>

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>

Author: Dorinda Bassey

config-libkrunfw_aarch64

@@ -2279,6 +2279,10 @@ CONFIG_VIRTIO_MENU=y
 CONFIG_VIRTIO_BALLOON=y
 # CONFIG_VIRTIO_MEM is not set
 CONFIG_VIRTIO_INPUT=y
+CONFIG_VIRTIO_RTC=y
+CONFIG_VIRTIO_RTC_PTP=y
+CONFIG_VIRTIO_RTC_ARM=y
+CONFIG_VIRTIO_RTC_CLASS=y
 CONFIG_VIRTIO_MMIO=y
 CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y
 CONFIG_VIRTIO_DMA_SHARED_BUFFER=y

config-libkrunfw_x86_64

@@ -1394,7 +1394,7 @@ CONFIG_EDAC_ATOMIC_SCRUB=y
 CONFIG_EDAC_SUPPORT=y
 CONFIG_RTC_LIB=y
 CONFIG_RTC_MC146818_LIB=y
-# CONFIG_RTC_CLASS is not set
+CONFIG_RTC_CLASS=y
 # CONFIG_DMADEVICES is not set
 
 #
@@ -1419,6 +1419,9 @@ CONFIG_VIRTIO_MENU=y
 CONFIG_VIRTIO_BALLOON=y
 # CONFIG_VIRTIO_MEM is not set
 CONFIG_VIRTIO_INPUT=y
+CONFIG_VIRTIO_RTC=y
+CONFIG_VIRTIO_RTC_PTP=y
+CONFIG_VIRTIO_RTC_CLASS=y
 CONFIG_VIRTIO_MMIO=y
 CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y
 # CONFIG_VDPA is not set