Bluetooth: Controller: Fix endianness issues for SyncInfo

Fix bitfield crossing byte boundary - replaced with macros for
setting/getting the values

Fix missing endianness conversion for evt_cntr

Changed aa from uint32_t to uint8_t[4] to align with the rest of
the code and avoid any potential endianness issues

Signed-off-by: Troels Nilsson <trnn@demant.com>