meta-agl-bsp: Update J7 EVM support for Kirkstone

meta-agl-bsp: Update J7 EVM support for Kirkstone

Changes:
- Rename machine template and related files to use j721e-evm instead
  of j7-evm to match meta-ti change.
- Update machine template to point into new meta-ti-bsp layer in the
  meta-ti repository.
- Drop local multiconfig TMPDIR tweak as it seems unrequired now,
  and is triggering a build failure around sysroot population that
  needs further investigation.  It may be added back in the future
  if the single TMPDIR again proves to have issues.

Bug-AGL: SPEC-3819

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I8c2717bb749735cfe36d86b48e3c61b1cca990e4