arm_adi_v5: add support for 64bit Class 0x9 ROM tables

arm_adi_v5: add support for 64bit Class 0x9 ROM tables

Arm documentation does not explicitly report the order of the two
32bit words that compose the 64bit value. But both ADIv5 and ADIv6
specify that only little-endian is supported (ADIv5.2 obsoletes
the big-endian support). This change reads the 64bit value in
little-endian.

Detect the 64bit content and use it.

Change-Id: I723ec099c7e8c70c1f9a568e32ea867fcbf1f1db
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6465
Tested-by: jenkins