aarch64: fix handling of 'reset halt'

aarch64: fix handling of 'reset halt'

Commit 6c0151623cb0 ("aarch64: add support for "reset halt"")
introduces the register setting to halt at reset vector, but:
- does not consider the case 'srst_pulls_trst' that makes useless
  setting the registers as they will be erased by the pulled trst;
- does not clean sticky errors in case of 'srst_gates_jtag'.

Avoid any register initialization on 'srst_pulls_trst' and move
the cleaning of sticky errors in the common block.

Change-Id: I6f839f06f7b091e234ede31ec18096e51f017bcd
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Fixes: 6c0151623cb0 ("aarch64: add support for "reset halt"")
Reviewed-on: https://review.openocd.org/c/openocd/+/7034
Tested-by: jenkins
Reviewed-by: Christian Hoff <christian.hoff@advantest.com>