kleidiai: Add SME vs SME2 distinction in kernel dispatch (#25478)

kleidiai: Add SME vs SME2 distinction in kernel dispatch (#25478)

The current integration treats SME as a single capability (CPU_FEATURE_SME)
with no distinction between SME(v1) and SME2. The kernels dispatched under
CPU_FEATURE_SME use SME2-specific instructions, making dispatch incorrect
on SME(v1)-only hardware.

We introduce build-time and runtime distinction between SME and SME2, and
wire SME(v1) and SME2 kernels based on actual hardware support.