arm64: dts: ti: k3-am642: Fix the L2 cache sets

A53's L2 cache[1] on AM642[2] is 256KB. A53's L2 is fixed line length
of 64 bytes and 16-way set-associative cache structure.

256KB of L2 / 64 (line length) = 4096 ways
4096 ways / 16 = 256 sets

Fix the l2 cache-sets.

[1] https://developer.arm.com/documentation/ddi0500/j/Level-2-Memory-System/About-the-L2-memory-system?lang=en
[2] https://www.ti.com/lit/pdf/spruim2

Fixes: 8abae938

 ("arm64: dts: ti: Add support for AM642 SoC")
Reported-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20211113043635.4296-1-nm@ti.com