AArch64: Allow additional sizes in prologue

AArch64: Allow additional sizes in prologue

When saving registers to the stack at the start of a function, not all state
needs to be saved. For example, only the first 64bits of float registers need
saving.  However, a program may choose to store extra state if it wishes,
there is nothing preventing it doing so.

The aarch64_analyze_prologue will error if it detects extra state being
stored.  Relex this restriction.

Tested via aarch64-prologue test.

gdb/ChangeLog:

	* aarch64-tdep.c (aarch64_analyze_prologue): Allow any valid
	register sizes.

gdb/testsuite/ChangeLog:

	* gdb.arch/aarch64-prologue.c: New test.
	* gdb.arch/aarch64-prologue.exp: New file.