MLECO-3546: Adding CMSIS pack with pidx file

Adding beta version of the CMSIS pack, created from the
main branch. Adding a corresponding PIDX file for this
pack to be linked to the public listing of Arm Keil packs.

Packs, pidx and related resources will be available under
'resources/cmsis-packs/' directory.

Change-Id: Iff6fe4d2a1cb14ae72442eb62664bf4ccd729c3c
Signed-off-by: Kshitij Sisodia <kshitij.sisodia@arm.com>