Add the target register read/write and memory dump debugfs interface

The debugfs interface reg_addr&reg_val used to read and write the target
register.
The interface mem_addr&mem_val used to dump the targer memory and also
can be used to assign value to target memory

The basic usage explain as below:

Register read/write:
reg_addr       (the register address)                    (read&write)
reg_value      (the register value,  output is ASCII)    (read&write)

Read operation:
1. Write the reg address to reg_addr
   IE:  echo 0x100000 > reg_addr
2. Read the value from reg_value
   IE:  cat reg_value
Write operation:
1. Write the reg address to reg_addr IE:  echo 0x100000 > reg_addr
2. Write the value to the reg_value  IE:  echo  0x2400 > reg_value

Target memory dump:
mem_addr (the memory address the length also can used as the second
paramenter address length)				(read&write)
mem_value (the content of the memory with the length, output is binary)
							(read&write)
Read operation:
1. Write the address and length to mem_addr
   IE:  echo 0x400000 1024 > mem_addr
2. Read the value from mem value, the output is binary format
   IE:  hexdump mem_value
Write operation:
1. Write the start mem address to mem_addr
   IE:  echo 0x400000 > mem_addr
2. Dump the binary value to the mem_value
   IE:  echo  0x2400 > mem_value or echo 0x2400 0x3400 ... > mem_addr
   (the value number should be separated with spacebar)

Signed-off-by: Yanbo Li <yanbol@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>