rdar://problem/10652076

Add logic to GDBRemoteRegisterContext class to be able to read/write a "composite" register
which has "primordial" registers as its constituents.  In particular, Read/WriteRegisterBytes()
now delegate to Get/SetPrimordialRegister() helper methods to read/write register contents.

Also modify RegisterValue class to be able to parse "register write" string value for the
NEON quadword registers which is displayed as a vector of uint8's.

Example:

(lldb) register write q0 "{0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 0x10}"
(lldb) register read q0
q0 = {0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 0x10}
(lldb) register read --format uint8_t[] s0
s0 = {0x01 0x02 0x03 0x04}
(lldb) register read --format uint8_t[] d0
d0 = {0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08}
(lldb) register read --format uint8_t[] d1
d1 = {0x09 0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 0x10}

llvm-svn: 151939