PR 33593 Misplaced synthetic plt symbols in aarch64 PIE binaries

elfNN_aarch64_plt_sym_val wrongly treats PIEs.  PIEs are an executable
but not ET_EXEC, instead being ET_DYN with DF_1_PIE set in DT_FLAGS_1
to distinguish them from shared libraries.

get_plt_type scans .dynamic for DT_AARCH64_BTI_PLT and
DT_AARCH64_PAC_PLT, setting PLT_BTI and PLT_PAC in the function return
value respectively.  It's easy enough to extend the .dynamic scan to
also return DF_1_PIE in tdata is_pie.

The patch also makes a few tidies, things I noticed when scanning all
the code dealing with sw_protections.plt_type.

	PR 33593
	* elfnn-aarch64.c (get_plt_type): Return DF_1_PIE via tdata is_pie.
	(elfNN_aarch64_plt_sym_val): Handle PIEs as well as ET_EXEC.
	(setup_plt_values): Delete wrong ET_EXEC comments.
	(elfNN_aarch64_late_size_sections): Remove excess parentheses.
	(elfNN_aarch64_finish_dynamic_sections): Rename type to plt_type,
	and simplify test for PLT_BTI or PLT_BTI_PAC.

Co-Authored-By: Michael Matz <matz@suse.de>