rtc: efi: add efi_procfs in efi_rtc_ops

Add efi_procfs in efi_rtc_ops to show rtc-efi info in /proc/driver/rtc.
Most of the code comes from efi_rtc_proc_show() in efirtc.

Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>