pru-icss_git.bb: add AM64x, update to PSSP v6.0.0
pru-icss_git.bb: add AM64x, update to PSSP v6.0.0

PRU Software Support Package (PSSP) v6.0.0 should be included in Linux Processor
SDK 8.1 for AM335x, AM437x, AM57x (if generated), AM64x, AM65x under
example-applications. For the release notes that come with v6.0.0, see
https://git.ti.com/cgit/pru-software-support-package/pru-software-support-package/tag/?h=v6.0.0

Linux Processor SDK 8.1 will be the first AM64x SDK release to include the PSSP.

PRU firmware will also be generated and placed in the default filesystem under
lib/firmware/pru.

Signed-off-by: Nick Saulnier <d4bfb656b68567590565db302ea52d6126aa258d@ti.com>
Signed-off-by: Yogesh Siraswar <e4c3dc570d04bd480366ad8aa87a4b23b1e4ce6e@ti.com>
Signed-off-by: Denys Dmytriyenko <d29de71aea38aad3a87d486929cb0aad173ae612@konsulko.com>
Signed-off-by: Yogesh Siraswar <e4c3dc570d04bd480366ad8aa87a4b23b1e4ce6e@ti.com>

rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti