tile: group .hottext* sections properly in vmlinux.lds

With this change such sections are grouped with regular text
in the vmlinux image; this change puts them at the front,
which is where the standard Linux includes .text.hot*.
This change should fix a recently-observed bug where a bunch of
symbols were being omitted from the /proc/kallsyms output
because they fell between _etext and _sinittext.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>