SAM3: Remove unused reference to SUPC registers

SAM3: Remove unused reference to SUPC registers

The SUPC (Supply Controller) registers are on different base addresses on different
SAM3 chips:
SAM3U: 0x400e1210
SAM3N: 0x400e1410
SAM3S: 0x400e1410

This creates a problem with the sam3_reg_list array which is const, but would need
to be changed at runtime to account for this variability. As this register is not
used anywhere, it's simplest to just remove it.

Change-Id: I987eb371648d826aa6d5e9de18d38c7bb66d6fca
Signed-off-by: Attila Kinali <attila@kinali.ch>
Reviewed-on: http://openocd.zylin.com/495
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>