This commit represents the second stage of the low power implementations
that are required from Mbed 5.10 onwards. Besides the default hal
implementations (rtc_api.c and sleep.c), the PL031 RTC's native driver
needed to be added. Due to HW limitations in SSE-050 and the CM3DS,
Deep Sleep couldn't be implemented, therefore it is functionally
identical to Sleep (WFI).
Change-Id: Ibed2bdb452f48c98024dc7ef07fb51a4425e0a80
Signed-off-by: Bence Kaposzta <bence.kaposzta@arm.com>