gdb: make avr_integer_to_address generate code or data address based on type

gdb: make avr_integer_to_address generate code or data address based on type

The AVR architecture is a Harvard one, meaning it has different memory
spaces for code and data.  In GDB, this is dealt with by having the data
(SRAM) addresses start at 0x00800000.  When interpreting an integer as
an address (converting to a CORE_ADDR), we currently always generate a
data address.  This doesn't work for some cases described below, where
the integer is meant to represent a code address.

This patch changes avr_integer_to_address so that it generates the
correct type of address (code or data) based on the passed type.

Using the simavr.exp board, I didn't see any regressions when running
the gdb.base/*.exp tests.  A few tests go from fail to pass, but none
from pass to fail.  There are a few new fails and unresolved, but it's
just because some tests manage to make more progress before failing in a
different way.

In practice, it fixes disassembling by address, as described in the PR:

    - (gdb) disassemble 0x12a,0x12b
    - Dump of assembler code from 0x12a to 0x12b:
    -    0x0000012a <main+0>: push    r28
    - End of assembler dump.

    + (gdb) disassemble 0x12a,0x12b
    + Dump of assembler code from 0x80012a to 0x80012b:
    +    0x0080012a:  nop
    + End of assembler dump.

And also, setting a breakpoint by address:

    - (gdb) p &main
    - $1 = (int (*)(void)) 0x12a <main>
    - (gdb) b *0x12a
    - Breakpoint 1 at 0x80012a

    + (gdb) p &main
    + $1 = (int (*)(void)) 0x12a <main>
    + (gdb) b *0x12a
    + Breakpoint 1 at 0x12a: file test-avr.c, line 3.
    + Note: automatically using hardware breakpoints for read-only addresses.

gdb/ChangeLog:

	PR gdb/13519
	* avr-tdep.c (avr_integer_to_address): Return data or code
	address accordingly to the second 'type' argument of the
	function.

Change-Id: Iaea1587d053e86f4ab8aebdcabec8d31a6d262cd