kernel: Add CONFIG_RTC to generic config

kernel: Add CONFIG_RTC to generic config

RTC (the legacy driver) should not really be used, but seems to crop up
after the kernel update. Fix this by disabling it in the generic config.

Fixes the following build issue seen in arm64 or powerpc64:

ARM JTAG DCC console (HVC_DCC) [N/y/?] n
Virtio console (VIRTIO_CONSOLE) [N/m/y/?] n
Enhanced Real Time Clock Support (legacy PC RTC driver) (RTC) [N/m/y/?] (NEW) aborted!

Console input/output is redirected. Run 'make oldconfig' to update configuration.

scripts/kconfig/Makefile:37: recipe for target 'silentoldconfig' failed

This should fix the build on the arm64/generic and the layerscape/64b
targets.

Fixes: 6c5c3a2edccf ("kernel: Update to version 4.4.182")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>