intelp2m: Add Go Managing Dependencies System support

intelp2m: Add Go Managing Dependencies System support

Add go.mod containing the full name of the project according to the
docs [1]: review.coreboot.org/coreboot.git/util/intelp2m, and also,
based on this, rename the internal packages to point to the absolute
path. This will allow Go Managing Dependencies System to integrate
packages from intelp2m to third-party Go written on the Go language [1].
This also requires fixing the Golang compiler version in go.mod: use
go1.18 [2], the latest up-to-date version.

[1] https://web.archive.org/web/20220910100342/https://go.dev/doc/modules/managing-dependencies
[2] https://web.archive.org/web/20220910100206/https://tip.golang.org/doc/go1.18

[ TEST ]
1) Import the coreboot project into some go project:

$cd path/to/go-project
$go get review.coreboot.org/coreboot.git
go: downloading review.coreboot.org/coreboot.git v0.0.0-20220903004133
-39914a50ae16
go: added review.coreboot.org/coreboot.git v0.0.0-20220903004133
-39914a50ae16

Thus, 'go get' correctly downloaded the contents of the repository.

2) Import intelp2m:

$cd path/to/go-project
$go get review.coreboot.org/coreboot.git/util/intelp2m
review.coreboot.org/coreboot.git/util/intelp2m imports
	./config: "./config" is relative, but relative import paths are
not supported in module mode
review.coreboot.org/coreboot.git/util/intelp2m imports
	./parser: "./parser" is relative, but relative import paths are
not supported in module mode

Thus, the problem is in the package names, but after this patch, the
import should be without errors.

3) Import a repository with an incorrect url:

$cd path/to/go-project
$go get review.coreboot.org/coreboot/test
go: unrecognized import path "review.coreboot.org/coreboot/test":
reading https://review.coreboot.org/coreboot/test?go-get=1:
404 Not Found

This has not happened in previous cases.

Change-Id: I12efae31227129b8c884af10fb233f398c4094e7
Signed-off-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64724
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>