Aarch64: Replace macro __x86_64__ with generic macro __LP64__

Aarch64: Replace macro __x86_64__ with generic macro __LP64__

Package wrt-plugins-common cannot be built for the architecture
aarch64 because of the following error:

error: 'std::string WrtDeviceApis::CommonsJavaScript::Converter::toString(std::size_t)' cannot be overloaded

For architecture x86_64 this error also occurs, but the build of
erroneous function is disabled by the use of macro __x86_64__, which
is defined when the build is performed for x86_64 architecture.

We decided to disable the build of this function for aarch64, too.
It is done by replacement of macro __x86_64__ with more generic macro
__LP64__, which is defined both for x86_64 and aarch64 or any other
64-bit architecture.

The build for other architectures has been verified in the following
OBS project:

https://build.tizen.org/project/show?project=devel%3Aarm_toolchain%3AMobile%3Atest

Change-Id: I73ddd310431d77ad3df2da60a37bc454f36d2e7f
Signed-off-by: Ilya Palachev <i.palachev@samsung.com>