runners: openocd: Reset target before running Elf

In case of flashing (which is typically used with OpenOCD)
we do reset of the target after programming application binary
in the non-volatile memory.

In case of Elf execution we need to reset the target before
loading Elf sections so that we might be sure our target
is in sane & expected state before we start execution.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>