omap: mailbox: convert rwlocks to spinlock
omap: mailbox: convert rwlocks to spinlock

rwlocks are slower and have potential starvation issues
therefore spinlocks are generally preferred.

see also: http://lwn.net/Articles/364583/

Signed-off-by: Ohad Ben-Cohen <f42ebdd520afb7505b40286b1d13fbb7281e5b96@wizery.com>
Signed-off-by: Kanigeri Hari <44b8f5bce5762b2245bded1d8007323b74b2cb21@ti.com>
Signed-off-by: Hiroshi DOYU <e891c4ae8deef7e6c0a3fb82004ec71ca9fb7e00@nokia.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs