The private libgcc is supported only on ARM, MIPS, PowerPC, SH, x86.
Those architectures should "select" HAVE_PRIVATE_LIBGCC and
CONFIG_USE_PRIVATE_LIBGCC should depend on it.

Currently, this option is enabled on Tegra boards and x86 architecture.
Move the definition from header files to Kconfig.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Tested-by: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Tom Warren <twarren@nvidia.com>