kbuild: do not quote string values in include/config/auto.conf

The previous commit fixed up all shell scripts to not include
include/config/auto.conf.

Now that include/config/auto.conf is only included by Makefiles,
we can change it into a more Make-friendly form.

Previously, Kconfig output string values enclosed with double-quotes
(both in the .config and include/config/auto.conf):

CONFIG_X="foo bar"

Unlike shell, Make handles double-quotes (and single-quotes as well)
verbatim. We must rip them off when used.

There are some patterns:

[1] $(patsubst "%",%,$(CONFIG_X))
[2] $(CONFIG_X:"%"=%)
[3] $(subst ",,$(CONFIG_X))
[4] $(shell echo $(CONFIG_X))

These are not only ugly, but also fragile.

[1] and [2] do not work if the value contains spaces, like
CONFIG_X=" foo bar "

[3] does not work correctly if the value contains double-quotes like
CONFIG_X="foo\"bar"

[4] seems to work better, but has a cost of forking a process.

Anyway, quoted strings were always PITA for our Makefiles.

This commit changes Kconfig to stop quoting in include/config/auto.conf.

These are the string type symbols referenced in Makefiles or scripts:

ACPI_CUSTOM_DSDT_FILE
ARC_BUILTIN_DTB_NAME
ARC_TUNE_MCPU
BUILTIN_DTB_SOURCE
CC_IMPLICIT_FALLTHROUGH
CC_VERSION_TEXT
CFG80211_EXTRA_REGDB_KEYDIR
EXTRA_FIRMWARE
EXTRA_FIRMWARE_DIR
EXTRA_TARGETS
H8300_BUILTIN_DTB
INITRAMFS_SOURCE
LOCALVERSION
MODULE_SIG_HASH
MODULE_SIG_KEY
NDS32_BUILTIN_DTB
NIOS2_DTB_SOURCE
OPENRISC_BUILTIN_DTB
SOC_CANAAN_K210_DTB_SOURCE
SYSTEM_BLACKLIST_HASH_LIST
SYSTEM_REVOCATION_KEYS
SYSTEM_TRUSTED_KEYS
TARGET_CPU
UNUSED_KSYMS_WHITELIST
XILINX_MICROBLAZE0_FAMILY
XILINX_MICROBLAZE0_HW_VER
XTENSA_VARIANT_NAME

I checked them one by one, and fixed up the code where necessary.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

nios2: fix building all dtbs

nios2 has a 'dtbs' target, but nothing is added to 'dtb-*' targets and
no dtbs were getting built. This enables building all the dts files in
arch/nios2/boot/dts/ when COMPILE_TEST and OF_ALL_DTBS are enabled.

Cc: Ley Foon Tan <lftan@altera.com>
Cc: nios2-dev@lists.rocketboards.org
Signed-off-by: Rob Herring <robh@kernel.org>

nios2: use common rules to build built-in dtb

Using the common build support for built-in dtb files just requires
adding a .dtb.o target to obj-y.

This has the side effect that CONFIG_NIOS2_DTB_SOURCE should now be just
the dts filename in arch/nios2/boot/dts/ directory. Before any path was
supported, but if you want to build in your dtb to the kernel, it should
be in the kernel tree.

Cc: Ley Foon Tan <lftan@altera.com>
Cc: nios2-dev@lists.rocketboards.org
Signed-off-by: Rob Herring <robh@kernel.org>

nios2: build .dtb files in dts directory

Align nios2 with other architectures which build the dtb files in the
same directory as the dts files. This is also in line with most other
build targets which are located in the same directory as the source.
This move will help enable the 'dtbs' target which builds all the dtbs
regardless of kernel config.

This transition could break some scripts if they expect dtb files in
the old location.

Cc: Ley Foon Tan <lftan@altera.com>
Cc: nios2-dev@lists.rocketboards.org
Signed-off-by: Rob Herring <robh@kernel.org>