i3c: mipi-i3c-hci: Relocate helper macros to HCI header file

The reg_* helper macros are currently limited to core.c. Moving them to
hci.h will allow their functionality to be utilized in other files outside
of core.c.

Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Co-developed-by: Guruvendra Punugupati <Guruvendra.Punugupati@amd.com>
Signed-off-by: Guruvendra Punugupati <Guruvendra.Punugupati@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20240829091713.736217-5-Shyam-sundar.S-k@amd.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>