gas: aarch64: Make chericap and capinit auto-align

gas: aarch64: Make chericap and capinit auto-align

Morello LLVM assumes that these directives should auto-align, it emits
assembly that does not explicitly align these directives.

Fix and testcases added.

gas/ChangeLog:

2021-07-29  Matthew Malcomson  <matthew.malcomson@arm.com>

	* config/tc-aarch64.c (s_aarch64_capinit, s_aarch64_chericap):
	Automatically align to 16 bytes.
	* testsuite/gas/aarch64/morello-capinit-align.s: New.
	* testsuite/gas/aarch64/morello-capinit-align.d: New.