imx6ull: rngb driver

[DawidSzpejna]

Add driver for rngb on imx6ull to support TRNG

Description

Motivation and Context

For imx6ull, trng wans't supported

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• [] My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[nalajcie]

pointed out some things which might be improved ;)

[gerard5]

Partial review, remarks for rngb_intr() function.

[ziemleszcz]

LGTM

[gerard5]

Here we are waiting for whether the self-test has finished or failed and not for all statuses, so shouldn't it be?

Suggested change

	while (common_rngb.intr_st == 0) {
	while ((common_rngb.intr_st & (SELF_TEST_DONE | ERROR_OCCURRED)) == 0) {

[gerard5]

Here we are waiting for whether the seeding has finished or failed and not for all statuses, so shouldn't it be?

Suggested change

	while (common_rngb.intr_st == 0) {
	while ((common_rngb.intr_st & (SEED_DONE | ERROR_OCCURRED)) == 0) {

[gerard5]

System cleanup is missing, any required resources freeing - if handleMsg() returns on msgRecv() error, also return 0 is misleading if handleMsg() terminates.