arm: move SYS_ARCH_TIMER to KConfig

SYS_ARCH_TIMER guards the usage of the ARM Generic Timer (aka arch
timer) in U-Boot.
At the moment it is mandatory for ARMv8 and used by a few ARMv7 boards.
Add a proper Kconfig symbol to express this dependency properly,
allowing certain board configuration to later disable arch timer in case
there are any problems with it.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[tuomas: rebase + fix conflicts and resync with moveconfig & use select]
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>

include/configs/mx7ulp_evk.h

@@ -46,7 +46,6 @@
 /* Using ULP WDOG for reset */
 #define WDOG_BASE_ADDR			WDG1_RBASE
 
-#define CONFIG_SYS_ARCH_TIMER
 #define CONFIG_SYS_HZ_CLOCK		1000000 /* Fixed at 1Mhz from TSTMR */
 
 #define CONFIG_INITRD_TAG

include/configs/qemu-arm.h

@@ -20,7 +20,6 @@
 #define CONFIG_SYS_MALLOC_LEN		SZ_16M
 
 /* For timer, QEMU emulates an ARMv7/ARMv8 architected timer */
-#define CONFIG_SYS_ARCH_TIMER
 #define CONFIG_SYS_HZ                       1000
 
 /* For block devices, QEMU emulates an ICH9 AHCI controller over PCI */

include/configs/stm32mp1.h

@@ -17,7 +17,6 @@
  * Number of clock ticks in 1 sec
  */
 #define CONFIG_SYS_HZ				1000
-#define CONFIG_SYS_ARCH_TIMER
 
 /*
  * malloc() pool size

include/configs/ti_armv7_keystone2.h

@@ -17,7 +17,6 @@
 
 /* SoC Configuration */
 #define CONFIG_ARCH_CPU_INIT
-#define CONFIG_SYS_ARCH_TIMER
 #define CONFIG_SPL_TARGET		"u-boot-spi.gph"
 #define CONFIG_SYS_DCACHE_OFF