keystore2: rename MonotonicRawTime to BootTime

Due to https://r.android.com/2822970 ("Use CLOCK_BOOTTIME for keystore2
auth token received time"), MonotonicRawTime now uses CLOCK_BOOTTIME
instead of CLOCK_MONOTONIC_RAW.  Therefore, rename it to BootTime.

Bug: 309686873
Test: atest -p --include-subdirs system/security/keystore2
Change-Id: If1fbbac2eccb03dc7360ae742d79e58f871fb80d
5 files changed