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

This patch implements functionalities of following ioctls:

RTC_WKALM_SET, RTC_WKALM_GET - Getting/Setting wakeup alarm

    Some RTCs support a more powerful alarm interface, using these
    ioctls to read or write the RTC's alarm time (respectively)
    with this structure:

        struct rtc_wkalrm {
            unsigned char enabled;
            unsigned char pending;
            struct rtc_time time;
        };

    The enabled flag is used to enable or disable the alarm
    interrupt, or to read its current status; when using these
    calls, RTC_AIE_ON and RTC_AIE_OFF are not used. The pending
    flag is used by RTC_WKALM_RD to report a pending interrupt
    (so it's mostly useless on Linux, except when talking to the
    RTC managed by EFI firmware). The time field is as used with
    RTC_ALM_READ and RTC_ALM_SET except that the tm_mday, tm_mon,
    and tm_year fields are also valid. A pointer to this structure
    should be passed as the third ioctl's argument.

Implementation notes:

    All ioctls in this patch have a pointer to a structure
    rtc_wkalrm 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 either of type
    'unsigned char' or 'struct rtc_time' (that was covered in one
    of previous patches), 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: <1579117007-7565-5-git-send-email-Filip.Bozuta@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

linux-user/syscall_types.h

@@ -266,6 +266,11 @@ STRUCT(rtc_time,
        TYPE_INT, /* tm_yday */
        TYPE_INT) /* tm_isdst */
 
+STRUCT(rtc_wkalrm,
+       TYPE_CHAR, /* enabled */
+       TYPE_CHAR, /* pending */
+       MK_STRUCT(STRUCT_rtc_time)) /* time */
+
 STRUCT(blkpg_ioctl_arg,
        TYPE_INT, /* op */
        TYPE_INT, /* flags */