arc: Get rid of even more debug prints

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
arc: Write back registers when dirty, not when invalid

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>
arc: Optimize jtag_write_block

Optimize jtag_write_block by not rewriting the transaction command register
for every word that we write.

Signed-off-by: Mischa Jonker <mjonker@synopsys.com>