cmake: support to create per-toolchain cmake file in SDK

cmake: support to create per-toolchain cmake file in SDK

The patch creates ${MULTIMACH_TARGET_SYS}-toolchain.cmake file
at ${SDK_INSTALL_DIR}/sysroots/${SDK_SYS}/usr/share/cmake/, which is
per-toolchain CMake toolchain file containing arch-specific values
and independent of OE environment variables.
The file gets created after installing SDK toolchain installer
ined by running "bitbake -c populate_sdk <image>".

The changes are similar to meson-setup.py which is used to
create arch-specific
${SDK_INSTALL_DIR}/sysroots/${SDK_SYS}/usr/share/meson/*-meson.cross

[YOCTO #14644]

Tested-by: Jan Dorniak <jaskij@gmail.com>
Signed-off-by: Jagadeesh Krishnanjanappa <workjagadeesh@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>