ARM: OMAP: DRA7: wakeupgen: Skip SAR save for wakeupgen

DRA7 has no SAR region for automated save and restore of wakeupgen,
which does not make real since the SoC really does not do legacy OFF
mode anymore. Further wakeupgen should never loose context in CSWR
retention mode for MPU domain on DRA7 since that is the deepest state
we will enter.

So, just skip, instead of oopsing as follows while attemptint to enter
suspend on BeagleBoard-X15.
[   55.589771] Unable to handle kernel paging request at virtual address 00002684
[   55.589771] pgd = ec69c000
[...]
[   55.589771] [<c0123cc8>] (irq_notifier) from [<c015ad70>] (notifier_call_chain+0x4c/0x8c)
[   55.589771] [<c015ad70>] (notifier_call_chain) from [<c021469c>] (cpu_cluster_pm_enter+0x2c/0x78)
[   55.589771] [<c021469c>] (cpu_cluster_pm_enter) from [<c0514508>] (syscore_suspend+0xb8/0x31c)
[   55.589771] [<c0514508>] (syscore_suspend) from [<c0197d24>] (suspend_devices_and_enter+0x308/0x9e4)
[   55.589771] [<c0197d24>] (suspend_devices_and_enter) from [<c0198a40>] (pm_suspend+0x640/0x75c)
[   55.589771] [<c0198a40>] (pm_suspend) from [<c0196bcc>] (state_store+0x64/0xb8)
[   55.589771] [<c0196bcc>] (state_store) from [<c0307914>] (kernfs_fop_write+0xc0/0x1bc)
[   55.589771] [<c0307914>] (kernfs_fop_write) from [<c028ac80>] (__vfs_write+0x1c/0xd8)
[   55.589771] [<c028ac80>] (__vfs_write) from [<c028bb70>] (vfs_write+0x90/0x16c)
[   55.589771] [<c028bb70>] (vfs_write) from [<c028c890>] (SyS_write+0x44/0x9c)
[   55.589771] [<c028c890>] (SyS_write) from [<c0107840>] (ret_fast_syscall+0x0/0x1c)
[...]

Signed-off-by: Nishanth Menon <nm@ti.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>