drivers/char: make efirtc.c driver explicitly non-modular

The Kconfig for this driver is currently:

config EFI_RTC
        bool "EFI Real Time Clock Services"

...meaning that it currently is not being built as a module by anyone.
Lets remove all modular references, so that when reading the driver
there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

We leave some tags like MODULE_LICENSE for documentation purposes.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>