ppc: fix endian check (#1029)

* Remove `big_endian` field of `cs_struct`

Added a helper macro `MODE_IS_BIG_ENDIAN()` to check if
`CS_MODE_BIG_ENDIAN` is set.

Refactored `cs_open()` check for valid mode out of arch-specific code
into arch-independent code. Also added a valid mode check to
`cs_option()`.  The checks use a new global array
`arch_disallowed_mode_mask[]`, which is initialized in the arch-specific
`*_enable()` functions.

Fixes bug where endianness could not be set for ppc.

* Fix Mac OS brew for Travis CI
15 files changed