Comment 0 for bug 1903087

Add the nitro_enclaves driver from mainline to linux-aws/{focal,bionic-5.4} and linux-aws/{groovy,hirsute}. The driver is supplied by the following mainline commits, which are all clean cherry picks for groovy with a couple of trivial backports for focal:

e82ed736ad2d MAINTAINERS: Add entry for the Nitro Enclaves driver
bf15d79ce142 nitro_enclaves: Add overview documentation
acc4229c3990 nitro_enclaves: Add sample for ioctl interface usage
0f5c7b748439 nitro_enclaves: Add Makefile for the Nitro Enclaves driver
07499cc661a9 nitro_enclaves: Add Kconfig for the Nitro Enclaves driver
9c8eb50fe9e2 nitro_enclaves: Add logic for terminating an enclave
111c775a5f0d nitro_enclaves: Add logic for starting an enclave
7dc9d4309fdb nitro_enclaves: Add logic for setting an enclave memory region
988b7a471726 nitro_enclaves: Add logic for getting the enclave image load info
ff8a4d3e3a99 nitro_enclaves: Add logic for setting an enclave vCPU
38907e124088 nitro_enclaves: Add logic for creating an enclave VM
bd47c995c0e4 nitro_enclaves: Init misc device providing the ioctl interface
e5d616d8bb50 nitro_enclaves: Handle out-of-band PCI device events
ad2b6980d0d3 nitro_enclaves: Handle PCI device command requests
89308c11ae3b nitro_enclaves: Init PCI device driver
1df624892c1e nitro_enclaves: Define enclave info for internal bookkeeping
0a44561768c5 nitro_enclaves: Define the PCI device interface
15b760c37ad3 nitro_enclaves: Add ioctl interface definition

linux-aws/focal also needs this prereq:

93ef1429e556 cpu/hotplug: Add new {add,remove}_cpu() functions

[Impact]

 * Supplies driver needed to support AWS feature.

[Test Case]

 * T.B.D. (to be validated by AWS).

[Regression Potential]

 * Low: Just adds a new driver module which won't load by default.