target: Correct profiling calculation

1. high_pc should be (maximum sample + 1) (Refer to gprof source code)
2. bucket index should be

     sample offset
    --------------- x (number of bucket)
	 sample range

For example, if minimum sample is 0 and maximum sample is 5
and the number of bucket is 3.

a = sampled_address - 0
b = 3
c = 6
(a, b, c refer to source code variables)

sampled_address = 0, => a = 0, => bucket_index = 0
sampled_address = 1, => a = 1, => bucket_index = 0
sampled_address = 2, => a = 2, => bucket_index = 1
sampled_address = 3, => a = 3, => bucket_index = 1
sampled_address = 4, => a = 4, => bucket_index = 2
sampled_address = 5, => a = 5, => bucket_index = 2

Change-Id: Ia9fa0e4d9c7183e3e9d7ceaf73e63729f07aa2ce
Signed-off-by: Hsiangkai Wang <hsiangkai@gmail.com>
Reviewed-on: http://openocd.zylin.com/1607


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>