xtensa: fix linker script transformation for .text.unlikely

Now that binutils generate *.unlikely sections which don't follow
documented (info as) literal section naming rules, section name
transformation script doesn't work well resulting in the following
errors at vmlinux link time:

	main.c:(.text.unlikely+0x3): dangerous relocation: l32r: literal
				     placed after use: .literal.unlikely

Fix section name transformation script by adding specific rule for
.text.unlikely sections.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>