ALSA: compress_offload: Add SNDRV_COMPRESS_AVAIL64 ioctl

The previous patch introduced a 64-bit timestamp ioctl
(SNDRV_COMPRESS_TSTAMP64). To provide a consistent API, this patch
adds a corresponding 64-bit version of the SNDRV_COMPRESS_AVAIL ioctl.

A new struct snd_compr_avail64 is added to the UAPI, which includes
the 64-bit timestamp. The existing ioctl implementation is refactored
to handle both the 32-bit and 64-bit variants.

Reviewed-by: Miller Liang <millerliang@google.com>
Tested-by: Joris Verhaegen <verhaegen@google.com>
Signed-off-by: Joris Verhaegen <verhaegen@google.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20250905091301.2711705-4-verhaegen@google.com