Fix curses on big endian hosts

Fix curses on big endian hosts

On big endian hosts, the curses interface is unusable: the emulated
graphic card only displays garbage, while the monitor interface displays
nothing (or rather only spaces).

The curses interface is waiting for data in native endianness, so
console_write_ch() should not do any conversion. The conversion should
be done when reading the video buffer in hw/vga.c. I supposed this
buffer is in little endian mode, though it's not impossible that the
data is actually in guest endianness. I currently have no big endian
guest to way (they all switch to graphic mode immediately).

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>