Add an IOCTL to check ION ABI version

Userspace needs a way to detect ION ABI version at runtime to determine
heap IDs. CURRENT_ION_ABI_VERSION is set to 2 considering legacy and
upstream versions as 0 and 1.

Bug: 140916230
Test: make

Signed-off-by: Hridya Valsaraju <hridya@google.com>

Change-Id: Ie9d9e23c2d8323620832906d33745d599cbce6be