i2c: xlp9xx: add support for Broadcom Vulcan

The Broadcom Vulcan ARM64 processor uses the same I2C controller
present on the Broadcom XLP9xx/5xx MIPS processor family.
Updated the Kconfig by adding ARCH_VULCAN option.

Signed-off-by: Tanmay Jagdale <tanmay.jagdale@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>