linux-user: Add support for enabling/disabling RTC features using ioctls

linux-user: Add support for enabling/disabling RTC features using ioctls

This patch implements functionalities of following ioctls:

RTC_AIE_ON, RTC_AIE_OFF - Alarm interrupt enabling on/off

    Enable or disable the alarm interrupt, for RTCs that support
    alarms.  The third ioctl's argument is ignored.

RTC_UIE_ON, RTC_UIE_OFF - Update interrupt enabling on/off

    Enable or disable the interrupt on every clock update, for
    RTCs that support this once-per-second interrupt. The third
    ioctl's argument is ignored.

RTC_PIE_ON, RTC_PIE_OFF - Periodic interrupt enabling on/off

    Enable or disable the periodic interrupt, for RTCs that sup‐
    port these periodic interrupts. The third ioctl's argument
    is ignored. Only a privileged process (i.e., one having the
    CAP_SYS_RESOURCE capability) can enable the periodic interrupt
    if the frequency is currently set above the value specified in
    /proc/sys/dev/rtc/max-user-freq.

RTC_WIE_ON, RTC_WIE_OFF - Watchdog interrupt enabling on/off

    Enable or disable the Watchdog interrupt, for RTCs that sup-
    port this Watchdog interrupt. The third ioctl's argument is
    ignored.

Implementation notes:

    Since all of involved ioctls have NULL as their third argument,
    their implementation was straightforward.

    The line '#include <linux/rtc.h>' was added to recognize
    preprocessor definitions for these ioctls. This needs to be
    done only once in this series of commits. Also, the content
    of this file (with respect to ioctl definitions) remained
    unchanged for a long time, therefore there is no need to
    worry about supporting older Linux kernel version.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Filip Bozuta <Filip.Bozuta@rt-rk.com>
Message-Id: <1579117007-7565-2-git-send-email-Filip.Bozuta@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>