tcl/target/ti_k3: Add a gdb-attach event hook for armv8 and simplify startup function

tcl/target/ti_k3: Add a gdb-attach event hook for armv8 and simplify startup function

Since we can detect the type of target as well, reuse the _cpu_no_smp_up
function name and use the target name to simplify the _up function and
maintain consistency with what we introduced for r5.

Lets introduce gdb-attach event in a much cleaner fashion.

NOTE: we add a halt 1000 to retain the default gdb-attach hook behavior

While at it, fix a minor type of s/are/as in "Set Default target are
core 0" and simplify the foreach usage.

Signed-off-by: Nishanth Menon <nm@ti.com>
Change-Id: I3259b7c3ae4c71b06d921edfaefe17c03bb673dc
Reviewed-on: https://review.openocd.org/c/openocd/+/6616
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>