Feature: TI ICEPick support

[dragonmux]

Detailed description

In this PR we introduce support for TI's ICEPick Type C which is found on the AM335x parts in front of the ADIv5 TAPs on the JTAG chain, allowing BMD to set the scan chain up to actually see any of the subsequent TAPs and enumerate them. This forms the basis too for the ICEPick Type D found on the TMS570, albeit with some differences.

NB: when a scan chain features an ICEPick on it, the debugger must not touch nRST ever, as doing so blows the ICEPick config away 🙃; similarly, if the scan chain features more than one component with one of these and they are anything other than the last item on the scan chan, things will also break and not work right. Scan is required to be restarted after (re-)configuring one of these and so messing with the scan chain geometry etc. This has deleterious effects in the JTAG discovery code if not right at the end.

Please also note that it is expected any future PRs that make use of this will rewrite this section of the Meson build file to properly specify the dependency. An example can be found as an experimental commit (permalinked here):

blackmagic/src/target/meson.build

Lines 378 to 394 in 70b7c6a

	target_ti_cortexa = declare_dependency(
	sources: files(
	'am335x.c',
	),
	compile_args: ['-DCONFIG_TI_SITARA=1'],
	dependencies: [target_cortexar, target_ti_icepick],
	)
	# If the Cortex-A/R target is not enabled, don't enable TI AM335x part support
	if enabled_targets.contains('cortexar')
	target_ti = [
	target_ti_cortexm,
	target_ti_cortexa,
	]
	else
	target_ti = target_ti_cortexm
	endif

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues

[esden]

LGTM