drivers/soc: Convert non-modular soc-realview to use builtin_platform_driver

This file depends on Kconfig SOC_REALVIEW which is a bool, so
we use the appropriate registration function, which avoids us
relying on an implicit inclusion of <module.h> which we are
doing currently.

While this currently works, we really don't want to be including
the module.h header in non-modular code, which we'd be forced
to do, pending some upcoming code relocation from init.h into
module.h.  So we fix it now by using the non-modular equivalent.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>