ARM: davinci: fix build failure without I2C

ARM: davinci: fix build failure without I2C

The two supplies are referenced outside of #ifdef CONFIG_I2C but
defined inside, which breaks the build if that is not built-in:

mach-davinci/board-dm644x-evm.c:861:21: error: use of undeclared identifier 'fixed_supplies_1_8v'
                                     ARRAY_SIZE(fixed_supplies_1_8v), 1800000);
                                                ^
mach-davinci/board-dm644x-evm.c:861:21: error: use of undeclared identifier 'fixed_supplies_1_8v'
mach-davinci/board-dm644x-evm.c:861:21: error: use of undeclared identifier 'fixed_supplies_1_8v'
mach-davinci/board-dm644x-evm.c:860:49: error: use of undeclared identifier 'fixed_supplies_1_8v'
        regulator_register_always_on(0, "fixed-dummy", fixed_supplies_1_8v,

I don't know if the regulators are used anywhere without I2C, but
always registering them seems to be the safe choice here.

On a related note, it might be best to also deal with CONFIG_I2C=m
across the file, unless this is going to be moved to DT and removed
really soon anyway.

Link: https://lore.kernel.org/r/20200527133746.643895-1-arnd@arndb.de
Fixes: 5e06d19694a4 ("ARM: davinci: dm644x-evm: Add Fixed regulators needed for tlv320aic33")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>