i2c: core: add api to provide frequency mode strings

mainline inclusion
from mainline-v5.12-rc7
3b4c747c
category: feature
bugzilla: 175140
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3b4c747cd32078172dd238929e38a43cfed83580



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Some I2C drivers like Designware and HiSilicon will print the
bus frequency mode information, so add a public one that everyone
can make use of.

Add the definition of the I2C Frequency Modes macro.

Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Reviewed-by: Jay Fang <f.fangjian@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>