xtensa: drop unused sections and remapped reset handlers

There are no .bootstrap or .ResetVector.text sections linked to the
vmlinux image, drop these sections from vmlinux.ld.S. Drop
RESET_VECTOR_VADDR definition only used for .ResetVector.text.

Drop remapped copies of primary and secondary reset vectors, as modern
gdb don't have problems stepping through instructions at arbitrary
locations. Drop corresponding sections from the corresponding linker
scripts.

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