rtc: move mc146818 helper functions out-of-line

The mc146818_get_time/mc146818_set_time functions are rather large
inline functions in a global header file and are used in several
drivers and in x86 specific code.

Here we move them into a separate .c file that is compiled whenever
any of the users require it. This also lets us remove the linux/acpi.h
header inclusion from mc146818rtc.h, which in turn avoids some
warnings about duplicate definition of the TRUE/FALSE macros.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>