Finish off functions mips32_pracc_read_mem16() and mips32_pracc_read_mem8()

Finish off functions mips32_pracc_read_mem16() and mips32_pracc_read_mem8()

This functions are unfinished and work only with  parameter count up to 1024.

Commands mdh and mdb from pic32mx context show values not related to memory
content if parameter count is bigger than 1024. Firt 1024 are ok.

Change-Id: Ie3f4d4a0f9d1d1a69bd3a18de2f72dd9249514cb
Signed-off-by: Salvador <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/550
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: jenkins