MIPS: Place __kernel_entry at the beginning of text section

Mark __kernel_entry as ".head.text" and place HEAD_TEXT before
TEXT_TEXT in the linker script. This ensures that __kernel_entry
will be placed at the beginning of text section.

Drop mips from scripts/head-object-list.txt.

Signed-off-by: Rong Xu <xur@google.com>
Reported-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Closes: https://lore.kernel.org/lkml/c6719149-8531-4174-824e-a3caf4bc6d0e@alliedtelesis.co.nz/T/


Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>