[IA64] fix "allnoconfig" build

Link errors:
arch/ia64/kernel/built-in.o: In function `arch_setup_dmar_msi':
(.text+0x35972): undefined reference to `dmar_msi_write'
... and more ...

because allnoconfig has CONFIG_DMAR=y due to the "select DMAR"
in arch/ia64/Kconfig under config IA64_GENERIC.

Drop that select, but add CONFIG_DMAR=y to generic_defconfig so
we keep testbuilding the DMAR code.
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/Kconfig

@@ -162,7 +162,6 @@ config IA64_GENERIC
 	select ACPI_NUMA
 	select SWIOTLB
 	select PCI_MSI
-	select DMAR
 	help
 	  This selects the system type of your hardware.  A "generic" kernel
 	  will run on any supported IA-64 system.  However, if you configure

arch/ia64/configs/generic_defconfig

@@ -234,3 +234,4 @@ CONFIG_CRYPTO_MD5=y
 # CONFIG_CRYPTO_ANSI_CPRNG is not set
 CONFIG_CRC_T10DIF=y
 CONFIG_MISC_DEVICES=y
+CONFIG_DMAR=y