drivers/misc/amd-sbi/Kconfig: select REGMAP_I2C

Without CONFIG_REGMAP, rmi-i2c.c fails to build because struct
regmap_config is not defined:

drivers/misc/amd-sbi/rmi-i2c.c: In function ‘sbrmi_i2c_probe’:
drivers/misc/amd-sbi/rmi-i2c.c:57:16: error: variable ‘sbrmi_i2c_regmap_config’ has initializer but incomplete type
57 | struct regmap_config sbrmi_i2c_regmap_config = {
| ^~~~~~~~~~~~~

Additionally, CONFIG_REGMAP_I2C is needed for devm_regmap_init_i2c():

ld: drivers/misc/amd-sbi/rmi-i2c.o: in function `sbrmi_i2c_probe':
drivers/misc/amd-sbi/rmi-i2c.c:69:(.text+0x1c0): undefined reference to `__devm_regmap_init_i2c'

Fixes: 013f7e7131bd ("misc: amd-sbi: Use regmap subsystem")
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Tested-by: Akshay Gupta <Akshay.Gupta@amd.com>
Reviewed-by: Akshay Gupta <Akshay.Gupta@amd.com>
Link: https://lore.kernel.org/r/20250829091442.1112106-1-max.kellermann@ionos.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>