Add EHRPWM and ECAP support build support for DAVINCI_DA8XX platforms.

Also, since DAVINCI platforms doesn't support TI-PWM-Subsystem module,
remove the select option for CONFIG_PWM_TIPWMSS.

Also, update CONFIG_PWM_TIPWMSS compiler directive appropriately in
pwm-tipwmss.h to fix the below compiler error upon removal of
CONFIG_PWM_TIPWMSS for DAVINCI platforms.

	drivers/pwm/pwm-tiecap.c: In function 'ecap_pwm_probe':
	drivers/pwm/pwm-tiecap.c:263:4: error: 'PWMSS_ECAPCLK_EN' undeclared
	(first use in this function)
	drivers/pwm/pwm-tiecap.c:263:4: note: each undeclared identifier
	is reported only once for each function it appears in
	drivers/pwm/pwm-tiecap.c:264:17: error: 'PWMSS_ECAPCLK_EN_ACK'
	undeclared (first use in this function)
	drivers/pwm/pwm-tiecap.c: In function 'ecap_pwm_remove':
	drivers/pwm/pwm-tiecap.c:291:49: error: 'PWMSS_ECAPCLK_STOP_REQ'
	undeclared (first use in this function)
	make[2]: *** [drivers/pwm/pwm-tiecap.o] Error 1
	make[1]: *** [drivers/pwm] Error 2
	make: *** [drivers] Error 2
Signed-off-by: Philip Avinash <avinashphilip@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>