Add pre-commit support for sanity checks

Use pre-commit framework [1] to run black and flake8 before the commit.
black and flake8 are managed by the pre-commit framework and they can be
run manually by the user using `pre-commit run` command.

Fix the code base with the help of black and flake8.
Fix import statements according to PEP8 guidelines [1]
Both tools have the following settings (specified in the pre-commit
configuration file):
* line length: 120 characters
* directory to exclude: ethosu/vela/tflite/ and ethosu/vela/ethos_u55_regs

Updated README.md on how to install pre-commit and how to run sanity checks.
Pipenv files have been updated including new dependencies for pre-commit.

[1]: https://www.python.org/dev/peps/pep-0008/#imports
[2]: https://github.com/pre-commit/pre-commit

Change-Id: I304d9fffdf019d390ffa396a529c8a7c2437f63d
Signed-off-by: Diego Russo <diego.russo@arm.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/Pipfile b/Pipfile
index 300bef65..33f941f5 100644
--- a/Pipfile
+++ b/Pipfile
@@ -4,6 +4,8 @@ url = "https://pypi.org/simple"
 verify_ssl = true
 
 [dev-packages]
+pre-commit = "*"
+ethos-u-vela = {editable = true,path = "."}
 
 [packages]
 ethos-u-vela = {editable = true,path = "."}