Add a GPROF=1 build option to enable gprof profiling for sandbox. This
adds the -pg flag to both compiler and linker when GPROF=1 is set,
following the same pattern as the existing FTRACE option.
Usage:
make GPROF=1 sandbox_defconfig all
./u-boot -T -c "ut dm"
...
gprof u-boot gmon.out
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
e77755ed85