Add Proliic new chip: PL2303TB & PL2303N(G)

Hi Johan & Greg,
Thansk for you check the patch file..

PL2303 is a general name on the market. In fact, PL2303 has the following various ICs.
A type: PL2303H,
B type: PL2303XA, PL2303HXA, PL2303HXB, PL2303HXC, PL2303HXD, PL2303EA, PL2303SA, PL2303RA, PL2303TA, PL2303TB
C type:PL2303HXN: PL2303GC, PL2303GS, PL2303GB, PL2303GT, PL2303GL, PL2303GE. <<--used different PID, different VENDOR_REQUEST

"Please split out in a separate patch and explain why it is needed. Alsoreplace the "magical" constants with descriptive defines."
I will push 3 patch file.

1. Support PL2303TB(old chip, B type), only add new VID_PID
2. Support PL2303HXD(old chip, B type), /* only support External Pull-Up Mode on PL2303HXD chip*. /
3. Support PL2303HXN(new chip, C type), add new VID_PID, new VENDOR_WRITE_REQUEST/ VENDOR_READ_REQUEST, new H/W, S/W flow control setting.