m68k: add missing SOFTIRQENTRY_TEXT linker section

Commit be7635e7 ("arch, ftrace: for KASAN put hard/soft IRQ entries
into separate sections") added a new linker section, SOFTIRQENTRY_TEXT,
to the linker scripts for most architectures. It didn't add it to any of
the linker scripts for the m68k architecture. This was not really a problem
because it is only defined if either of CONFIG_FUNCTION_GRAPH_TRACER or
CONFIG_KASAN are enabled - which can never be true for m68k.

However commit 229a7186 ("irq: Make the irqentry text section
unconditional") means that SOFTIRQENTRY_TEXT is now always defined. So on
m68k we now end up with a separate ELF section for .softirqentry.text
instead of it being part of the .text section. On some m68k targets in some
configurations this can also cause a fatal link error:

  LD      vmlinux
/usr/local/bin/../m68k-uclinux/bin/ld.real: section .softirqentry.text loaded at [0000000010de10c0,0000000010de12dd] overlaps section .rodata loaded at [0000000010de10c0,0000000010e0fd67]

To fix add in the missing SOFTIRQENTRY_TEXT section into the m68k linker
scripts. I noticed that m68k is also missing the IRQENTRY_TEXT section,
so this patch also adds an entry for that too.

Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>