platform/chrome: cros_ec_lpc: introduce a priv struct for the lpc device

lpc_driver_data stores the MMIO port base for EC mapped memory.
cros_ec_lpc_readmem uses this port base instead of hardcoding
EC_LPC_ADDR_MEMMAP.

Signed-off-by: Dustin L. Howett <dustin@howett.net>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Mario Limonciello <superm1@gmail.com>
Link: https://lore.kernel.org/r/20240403004713.130365-2-dustin@howett.net


Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>