Include I2C constants to fix Unicorne build

[bcat]

Description

The Unicorne keyboard that was recently merged (#12993) no longer builds at latest master due to some undefined I2C constants:

Compiling: keyboards/yanghu/unicorne/unicorne.c                                                    In file included from ./lib/chibios/os/hal/include/hal_pal.h:174,
                 from ./lib/chibios/os/hal/include/hal.h:139,
                 from tmk_core/common/chibios/platform_deps.h:18,
                 from quantum/quantum.h:18,
                 from keyboards/yanghu/unicorne/unicorne.h:19,
                 from keyboards/yanghu/unicorne/unicorne.c:16:
keyboards/yanghu/unicorne/unicorne.c: In function 'i2c_init':
keyboards/yanghu/unicorne/unicorne.c:26:23: error: 'I2C1_SCL_BANK' undeclared (first use in this function); did you mean 'I2C_CR1_ACK'?
         palSetPadMode(I2C1_SCL_BANK, I2C1_SCL, PAL_MODE_INPUT);
                       ^~~~~~~~~~~~~

(And similar errors follow.) Looks like including i2c_master.h pulls in the relevant definitions. I've verified that qmk compile -kb yanghu/unicorne/f411 -km all builds successfully with this fix.

@yanghu, does this look good to you?

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Unicorne keyboard fails to build at latest master.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

Just a heads up, this is fixed in develop, already, which is due to merge in about 2 weeks.

[bcat]

Just a heads up, this is fixed in develop, already, which is due to merge in about 2 weeks.

Ah, I didn't realize that. Should I drop this PR then?

[drashna]

Nah, it may still be helpful to get it in sooner rather than later.

[bcat]

Looks like 2021Q4 breaking changes are merged now, so I'll go ahead and close this. :)