xtensa: optimize local_flush_tlb_kernel_range

Don't flush whole TLB if only a small kernel range is requested.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: add HIGHMEM support

Introduce fixmap area just below the vmalloc region. Use it for atomic
mapping of high memory pages.
High memory on cores with cache aliasing is not supported and is still
to be implemented. Fail build for such configurations for now.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: xtfpga: introduce SoC I/O bus

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: add support for KC705

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>