Handle endianness in the Opcode class

Previously, an opcode set via SetOpcode32 (for example) was later
extracted via GetData() as a byte sequence in host order rather than
target order.

Review: http://llvm-reviews.chandlerc.com/D1838


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196808 91177308-0d34-0410-b5e6-96231b3b80d8