[kernel][dev][intel-rng] C -> CPP file conversion

Minimal changes and a clang-format pass.

There's a buffer overflow bug that will be fixed in the next change.

Change-Id: I2a1eece67bc0ad128c537f8368aa8533d5b1acc1
Testing: validate that the driver builds and generates random bits.

[build] flatten the build

Previously we treated kernel/, system/, and third_party/ as
overlays on a shared namespace. This required the concept
of "canonical" module names, and a lot of complexity to ensure
that things didn't collide and the build worked.

This change gets rid of that, no longer passes -I to make,
so that include directives from our *.mk files do not magically
wildcard across various paths, etc.

The most user-visible change is that everywhere where a module
name is specified (MODULE_DEPS, MODULE_LIBS, etc), full module
names like kernel/lib/io or system/ulib/mxio must be used instead
of previously-allowed "short" names like lib/io and ulib/mxio.

The build output still has a similar shape, but the first segment
of the module path (kernel/, system/, or third_party/) is no
longer elided under $(BUILDDIR)

Change-Id: I525aba1da1c86eb7a86007bddc669f7eeebfedd5

[kernel][dev][intel_rng] Use compiler intrinsics

The compilers provide standard intrinsics for the rdrand and
rdseed instructions. Use them instead of inline asm. Use of
these intrinsics was previously disabled because of a code
generation bug in GCC-6.2.0 (still present in 6.3.0 as released).
The new GCC-6.3.0 toolchain includes the backported upstream fix
for that bug, so use of the intrinsics should now be safe (and
always was in the Clang build).

Change-Id: Id8c1e38bf454a91d4adec389747362979fcda964

[kernel][dev][intel-rng] Use _rdseed64_step intrinsic

The compiler has an intrinsic for this, for which it
generates slightly better code than inline asm can do.

Change-Id: I27da73cc47414707948c4fed43c48c2508d71c5d

[x86] Add an RDSEED based entropy source

Change-Id: I196435dd34823358d2426e4deeba32b329fb38e1