tcl/target/ls1088: Break out common configuration

tcl/target/ls1088: Break out common configuration

Several Layerscape processors (LS1088A, LS2088A, LS2160A, and LS1028A)
share a common architecture. Break out the common setup from the LS1088
config in preparation for adding the LS1028A. There's no official name
for this series of processors, but NXP refers to them as "chassis
generation 3" in U-Boot, so we'll go with that too.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Change-Id: Ic6f89f95c678101f54579bcaa5d79c5b67ddf50a
Reviewed-on: https://review.openocd.org/c/openocd/+/6975
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>