linux-user: Add support for getting/setting RTC time and alarm using ioctls

linux-user: Add support for getting/setting RTC time and alarm using ioctls

This patch implements functionalities of following ioctls:

RTC_RD_TIME - Getting RTC time

    Returns this RTC's time in the following structure:

        struct rtc_time {
            int tm_sec;
            int tm_min;
            int tm_hour;
            int tm_mday;
            int tm_mon;
            int tm_year;
            int tm_wday;     /* unused */
            int tm_yday;     /* unused */
            int tm_isdst;    /* unused */
        };

    The fields in this structure have the same meaning and ranges
    as the tm structure described in gmtime man page. A pointer
    to this structure should be passed as the third ioctl's argument.

RTC_SET_TIME - Setting RTC time

    Sets this RTC's time to the time specified by the rtc_time
    structure pointed to by the third ioctl's argument. To set
    the RTC's time the process must be privileged (i.e., have the
    CAP_SYS_TIME capability).

RTC_ALM_READ, RTC_ALM_SET - Getting/Setting alarm time

    Read and set the alarm time, for RTCs that support alarms.
    The alarm interrupt must be separately enabled or disabled
    using the RTC_AIE_ON, RTC_AIE_OFF requests. The third
    ioctl's argument is a pointer to a rtc_time structure. Only
    the tm_sec, tm_min, and tm_hour fields of this structure are
    used.

Implementation notes:

    All ioctls in this patch have pointer to a structure rtc_time
    as their third argument. That is the reason why corresponding
    definition is added in linux-user/syscall_types.h. Since all
    elements of this structure are of type 'int', the rest of the
    implementation is straightforward.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Filip Bozuta <Filip.Bozuta@rt-rk.com>
Message-Id: <1579117007-7565-3-git-send-email-Filip.Bozuta@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>