tty: amiserial: Fix namespace collision and startup() section placement with -ffuncti...

tty: amiserial: Fix namespace collision and startup() section placement with -ffunction-sections

When compiled with -ffunction-sections (e.g., for LTO, livepatch, dead
code elimination, AutoFDO, or Propeller), the startup() function gets
compiled into the .text.startup section (or in some cases
.text.startup.constprop.0 or .text.startup.isra.0).

However, the .text.startup and .text.startup.* sections are also used by
the compiler for __attribute__((constructor)) code.

This naming conflict causes the vmlinux linker script to wrongly place
startup() function code in .init.text, which gets freed during boot.

Some builds have a mix of objects, both with and without
-ffunctions-sections, so it's not possible for the linker script to
disambiguate with #ifdef CONFIG_FUNCTION_SECTIONS or similar.  This
means that "startup" unfortunately needs to be prohibited as a function
name.

Rename startup() to rs_startup().  For consistency, also rename its
shutdown() counterpart to rs_shutdown().

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/9e56afff5268b0b12b99a8aa9bf244d6ebdcdf47.1763669451.git.jpoimboe@kernel.org