arm64: dts: imx8mp: remove arm,primecell-periphid at etm nodes

The reg size of etm nodes is incorrectly set to 64k instead of 4k. This
leads to a crash when calling amba_read_periphid().  After corrected reg
size, amba_read_periphid() retrieve the correct periphid.
arm,primecell-periphid were removed from the etm nodes.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>