xtensa: fix build errors with cache functions

() arch_icache_line_size_get() needs to be inlined or else
   compiler would complain that it is not being used.
() arch_icache_flush_all() returns -ENOTSUP not as there is
   no xthal_icache_all_writeback() in HAL.
() Fix typo vid -> void in arch_icache_disable().

Signed-off-by: Daniel Leung <daniel.leung@intel.com>