gdb/hppa-tdep.c: Fix logical working flow issues and check additional store instructions.

gdb/hppa-tdep.c: Fix logical working flow issues and check additional store instructions.

Original working flow has several issues:

 - typo issue: "(inst >> 26) == 0x1f && ..." for checking 'stw(m)'.

 - "(inst >> 6) == 0xa" needs to be "((inst >> 6) & 0xf) == 0xa".

And also need check additional store instructions:

 - For absolute memory: 'stby', 'stdby'.

 - For unaligned: 'stwa', 'stda'.

The original code also can be improved:

 - Remove redundant double check "(inst >> 26) == 0x1b" for 'stwm'.

 - Use 2 'switch' statements instead of all 'if' statements.

	* hppa-tdep.c (inst_saves_gr): Fix logical working flow issues
	and check additional store instructions.