power: smb1360: Add a debugfs entry to dump FG registers

Add a debugfs node to dump
FG scratch pad registers - Address 0x80 to 0xFF
FG config registers - Address 0x24 to 0x2F
FG Shadow registers - Address 0x60 to 0x6F

Change-Id: I6ad0bd0d2f22bd7c50ec9fe7ea568f1302608a81
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>